Hart was asked to start out in the WWF with a cowboy gimmick but refused, citing that where he comes from "if you say you're a cowboy, you'd better be one". He instead requested to be paired with his brother-in-law Jim "The Anvil" Neidhart who was being managed by Jimmy Hart and asked to be called the Hart Foundation. He made his first televised WWF debut in August 1984, in a tag team match where he teamed with his brother-in-law, The Dynamite Kid. In 1985, he was eventually partnered up with another brother-in-law, Neidhart, to build the promotion's tag team division. Originally a heel team, they joined manager Jimmy Hart's Hart Foundation stable but soon the name stuck with the team of Bret and Anvil, due to the similar family names of both team members and their manager. At WrestleMania 2, they participated in a 20-man battle royal which was won by André the Giant. Bret's agile, technical style—which earned him the moniker "The Excellence of Execution" (coined by Gorilla Monsoon)—created an intriguing contrast with his partner Neidhart's strength and brawling skills.
Hart rose to fame in the WWF in the mid 1980s, and the Hart Foundation won the WWF Tag Team Championship twice. Their first reign started on the February 7, 1987 edition of Superstars when they defeated the British Bulldogs to win the title. They lost the title to Strike Force on the October 27 edition of Superstars. Eventually, they turned face and adopted the nickname "The Pink and Black Attack."
At SummerSlam, the Hart Foundation began their second reign by defeating Demolition members Crush and Smash in a two out of three falls match with some help from the Legion of Doom. On October 30, the Hart Foundation lost the title to The Rockers (Marty Jannetty and Shawn Michaels), but a few days later, President Jack Tunney returned the title to the Hart Foundation because the decision had been reversed due to a rope coming off of the turnbuckle during the match and the win was never acknowledged on television. The Hart Foundation's reign lasted from August 27, 1990 to March 24, 1991.
During his time in the Hart Foundation, Hart also competed occasionally as a solo wrestler. At WrestleMania IV he was the last man eliminated in a battle royal, by the winner Bad News Brown. Brown also defeated Hart in a singles match at Wrestlefest 88. In May 1989 Hart won a 16-man battle royal in Hamilton, Ontario.
Following a loss to The Nasty Boys at WrestleMania VII, the Foundation split and Hart went on to pursue a singles career. He won his first WWF Intercontinental Championship by defeating Mr. Perfect with the Sharpshooter at SummerSlam in 1991. Hart was then placed in a feud with the Mountie. This feud came about when the Mountie's manager, Jimmy Hart, threw water on Hart. Then, the Mountie proceeded to shock Hart with a cattle prod. Following the loss, Roddy Piper defeated Mountie with a sleeper hold at the 1992 Royal Rumble, and Bret would later pin Piper for his second Intercontinental Championship at WrestleMania VIII later that year.
In July 1992, Hart defeated Shawn Michaels in the first ever ladder match in the World Wrestling Federation. While many remember Michaels as the main innovator of the ladder match due to his later success in those matches, it was actually Hart who introduced this match format to the WWF.
Hart dropped the Intercontinental Championship to his brother-in-law, Davey Boy Smith, in the main event of SummerSlam in 1992 held before over 80,000 fans at Wembley Stadium. It was his first main event pay-per-view match, and he subsequently maintained main event status, being pushed as a contender to the WWF Championship. He won the WWF Championship from Ric Flair at Saskatchewan Place in Saskatoon, Saskatchewan on October 12 of that year, in a match not originally broadcast on WWF television—the match was instead available on a Coliseum Video release. Hart dislocated one of the fingers on his right hand during the match and popped it back in himself so it would not affect the rest of the match.Hart defended the title against contenders such as Papa Shango, Shawn Michaels, and Razor Ramon before losing the title to Yokozuna at WrestleMania IX after interference from Mr. Fuji. Mr. Fuji then challenged Hulk Hogan, who had come out to help Hart, to compete for the title; Hogan then won his fifth WWF Championship from Yokozuna. Shortly after, however, Hart won the first pay-per-view King of the Ring tournament in 1993, defeating Razor Ramon, Mr. Perfect, and Bam Bam Bigelow (prior King of the Ring tournaments were just house show events). After being crowned as the King of the Ring, Hart was attacked by announcer Jerry "The King" Lawler. Lawler claimed he was the rightful King and began a barrage against Hart and his family. The feud culminated in a match between the two at SummerSlam in 1993, where Hart originally won the match by submission, via the Sharpshooter. Hart, however, would not let go of the hold and the decision was reversed to a Lawler victory by disqualification. According to Hart, the original plan for SummerSlam was to pit WWF Champion Hulk Hogan against Hart in a passing of the torch. Hart also claimed that promotional photos were even taken of the two playing tug of war with the belt before the plans were dropped. Instead, Hogan dropped the belt to Yokozuna in his last WWF appearance at the King of the Ring PPV, which inspired some genuine animosity between the two as Hart felt that Hogan didn't respect him enough to drop the belt and put Bret over as the leader of the "new WWF Generation."
It was at this point that Bret Hart entered into a feud with his younger brother, Owen Hart. The storyline involved Owen becoming jealous of Bret. It began at Survivor Series, when the Harts (Bret, Owen, Bruce, and Keith) took on Shawn Michaels (a last-minute substitution for Lawler) and his knights. All of the brothers survived the match except for Owen, the only Hart family member eliminated. Owen blamed Bret for his elimination and in the weeks ahead, blamed Bret for holding him back. Owen demanded a one-on-one match with Bret, which Bret refused to accept. In the storyline, Bret, along with his parents, worked over the Christmas holidays to reunite the family and to settle their rivalry.
At the Royal Rumble in January, Bret and Owen took on The Quebecers for the WWF Tag Team Championship. Referee Tim White stopped the match after he considered Bret unable to continue after he sustained a kayfabe knee injury during the match. After the match, Owen berated his brother for costing him a title opportunity and attacked the injured knee, setting the feud between the two. Later on, Hart managed to participate and win the 1994 Royal Rumble match amid controversy. Hart and Lex Luger were the final two participants and the two were eliminated over the top rope at the same time. Therefore, both men were named co-winners of the 1994 Royal Rumble match and received title shots at WrestleMania X. Luger won the chance to face Yokozuna first, with Hart having to wrestle his brother Owen, who still demanded a match, before receiving his title shot. Owen won the match. Hart lost his match against Owen but went on to defeat Yokozuna for his second WWF Championship.
Hart continued to feud with his brother Owen while he also started feuding with Diesel. Hart's friend and former tag team partner Jim Neidhart returned to the WWF and reunited with Hart. At King of the Ring, Hart defended the WWF Championship against Diesel. When Hart was winning the match, Shawn Michaels interfered on Diesel's behalf. Diesel appeared close to victory after he delivered a Jackknife Powerbomb yet before he could pin Hart, Neidhart interfered. Diesel won by disqualification but Hart retained his title. Neidhart left when Diesel and Michaels attacked Hart following the match. Neidhart's motivation was made clear when he helped Owen win the tournament that night, so that he could receive a title shot against his brother. At SummerSlam, Hart successfully retained the WWF Championship against Owen in a steel cage match. This match would get a 5-star rating from Dave Meltzer.
Hart eventually lost his WWF Championship at Survivor Series in a submission match against Bob Backlund where the manager of either competitor (Davey Boy Smith for Hart, Owen for Backlund) would have to 'throw in the towel' for the wrestler they were representing. When Hart was in Backlund's Crossface Chickenwing and Davey Boy was kayfabe knocked out, Owen persuaded his mother Helen to throw in the towel for Hart, giving Backlund the championship victory. Bret's feud with Backlund would continue at WrestleMania XI where he would defeat Backlund in another submission match.
Bret would then go after Diesel's WWF Championship in 1995. After their match at the Royal Rumble was continually marred by outside interference, Bret won his third WWF Championship at Survivor Series in a No DQ match against Diesel. After Hart's real-life rival Shawn Michaels won the 1996 Royal Rumble, a 60 minute Iron Man match was set up between the two at WrestleMania XII. The wrestler with the most decisions during the 60 minutes would win the match and the WWF Championship. With less than a minute left on the clock and the score still 0–0, Michaels jumped from the middle rope; his legs were caught by Hart, and Hart locked in his Sharpshooter. However, Michaels did not submit in the last 30 seconds so the match ended in a tie. President Gorilla Monsoon ruled that the match would continue in sudden death overtime. Michaels hit a superkick to win the gold.
Hart left the WWF in March 1996. He would consider offers of employment from both WCW and the WWF, but would ultimately re-sign with the WWF. Over the summer, Steve Austin, who was fresh from winning the 1996 King of the Ring, continually taunted Bret and challenged him to come back and have a match. After an eight-month absence, Bret returned and defeated Austin at Survivor Series. The feud continued at the Royal Rumble, when Hart tossed Austin out of the ring, only for Austin (unbeknownst to the referees) to climb back into the ring and win the Rumble. In order to deal with this controversy, a Fatal Four-Way between Austin and the participants he eliminated after reentering the ring was set up for In Your House 13: Final Four, with the winner becoming the number one contender. After current champion Shawn Michaels relinquished the belt, though, the match officially became one for the WWF Championship. Hart defeated Austin, Vader, and The Undertaker in the Fatal Four-Way. However, Austin made sure Hart's reign was short-lived, costing him a match against Sycho Sid the next night on Raw. The two had a steel cage match shortly before WrestleMania 13 (Hart's twelfth consecutive and final WrestleMania), which saw Austin actually attempt to help Hart win, in order to make their match at WrestleMania 13 a title match. Concurrently, The Undertaker, who had a scheduled match with Sid at WrestleMania, attempted to help Sid win. Sid ultimately retained, leading to a pure grudge match for Hart and Austin.
At WrestleMania 13, Hart and Austin had their rematch in a Submission match that would later get a 5-star rating from Dave Meltzer. In the end, Hart locked the Sharpshooter on a bloody Austin, who refused to give up. In fact, Austin never quit, but passed out from the blood loss and pain. Ken Shamrock, the special guest referee, awarded Hart the match, after which he continued to assault Austin. This turned Austin face, and Hart became a heel. The original plan for WrestleMania 13 was a Hart versus Michaels championship rematch in which Michaels was slated to drop the belt to Hart. However, Michaels injured his knee two weeks after the Royal Rumble. Rumors immediately began flying that Shawn did not want to drop the belt to Bret. Hart actually came out during the main event at WrestleMania 13 and challenged Michaels to step in the ring and stated (in a shoot promo) that Michaels had a "pussy foot injury." McMahon, commentating at ringside alongside Michaels, immediately got up from his seat and tried to keep Michaels calm. Hart would face Austin once again in the main event of In Your House 14, in which Austin was victorious via disqualification.
In the ensuing weeks, Bret "The HitMan" Hart denounced American fans, because of their negative reaction to him in the recent weeks in contrast to his continued popularity through the rest of the world, and reunited with brother Owen and brothers-in-law Davey Boy Smith and Jim Neidhart. The family members formed a new Hart Foundation with Brian Pillman; this incarnation was an anti-American stable which was popular within Canada and Europe. During an angle in which it appeared that the Hart Foundation had vandalized the locker room of the African American stable, the Nation of Domination (in the storyline, DX framed the Hart Foundation). As kayfabe retaliation, during a promo with DX, Hart called both Triple H and Shawn Michaels "homos". After leaving the WWF, Hart apologized for the angles and said that he had been pressured into going through with them. He said, "I am not in any shape or form a racist. And I don't believe it is anything to kid around about. I also want to apologize for any remarks I made about gay people. It was a stupid mistake on my part." Hart's reluctance to use such references was cited on Wrestling with Shadows, where he points out that while Shawn Michaels wanted Bret to use these insults against him to further their on-air feud, Bret was extremely reluctant to do so.
Hart captured his fifth WWF Championship at SummerSlam after spitting in guest referee Shawn Michaels' face; Michaels swung a steel chair in retaliation, which accidentally struck the Undertaker and allowed Hart to get the pin.
Around this time, Hart's on-air rivalry with "announcer" Vince McMahon also escalated. A heated ringside altercation between the two led many fans to dislike McMahon, who at the time was being exposed as owner of the WWF more and more frequently on-air. Although Hart had signed a 20-year contract back in 1996, McMahon had asked him to talk to World Championship Wrestling (WCW) about possibly taking a second look at their original offer to him, as the WWF was in a rough financial position at the time and could not afford the contract. Hart's final match with the WWF would be a title match against his rival, Shawn Michaels at Survivor Series in Montreal. Hart did not want to end his WWF career with a loss to Michaels in his home country; McMahon agreed to Hart's idea of forfeiting the championship the next night on Raw or losing it a few weeks later.
Although Hart stated to McMahon he would not take the WWF Championship with him to WCW TV (and despite insistence from then-WCW President Eric Bischoff, according to Hart's DVD biography, that Hart would join WCW with a "clean slate"), McMahon was still concerned; this led to him breaking his word in what eventually came to be known as the Montreal Screwjob. Even though Hart did not submit to the Sharpshooter, referee Earl Hebner called for the bell as if he had, on McMahon's orders. This resulted in Hart "losing" the WWF Championship to Michaels. The night ended with an irate Hart spitting in McMahon's face, destroying television equipment, and punching McMahon backstage in front of Gerald Brisco, Pat Patterson, and McMahon's son Shane. Hart also confronted Michaels backstage about the match finish. Many behind-the-scenes events leading up to the Montreal Screwjob were filmed for the documentary Hitman Hart: Wrestling with Shadows, released in 1998.
A day after the Survivor Series pay-per-view, Eric Bischoff, while with the New World Order (nWo), announced that Hart was going to be coming to World Championship Wrestling (WCW), and joining the nWo. About a month after Survivor Series, Hart joined WCW, the WWF's main competitor. He made his debut on WCW Monday Nitro on December 15, 1997 when it was announced by WCW Chairman of the Board J.J. Dillon that Hart would be the special guest referee for the match between Bischoff and Larry Zbyszko at Starrcade. Bret was involved in the Sting versus Hulk Hogan match at Starrcade, stepping in toward its conclusion as impromptu referee. He attacked referee Nick Patrick, accusing him of making a fast count and shouting he would not let "it happen again" (a reference to the Montreal Screwjob). During Bischoff's period in control of the company, the goodwill towards Hart generated by the Montreal Screwjob resulted in his being pushed as a face; he defeated Ric Flair in his first WCW match at Souled Out in 1998, and beat Curt Hennig at Uncensored.
However, Hart's WCW face run was short-lived, and in April 1998 he turned heel in a Nitro main event involving Hogan and "Macho Man" Randy Savage, unofficially joining the nWo. He defeated Savage in singles action at Slamboree, thanks to assistance from Hogan, and then again in a tag team match with Hogan at The Great American Bash in which Savage was partnered with Roddy Piper. At Bash at the Beach, Hart competed in his first championship match in WCW as he faced Booker T for Booker's WCW World Television Championship. He was disqualified after hitting Booker with a steel chair.Although an established main event level star and five-time world champion in the WWF, Hart had entered WCW amid a struggle for the WCW World Heavyweight Championship among the promotion's top stars. WCW management therefore decided to book Hart to win the promotion's second most prestigious title, the WCW United States Heavyweight Championship, instead. Although Hart would later become a two-time WCW World Heavyweight Champion, some wrestling critics saw WCW's failure to push Hart as a contender to the title for another year—despite previously being one of the WWF's top stars and having signed an estimated $3 million a year contract with WCW—as a mistake. Vince McMahon echoed this sentiment, claiming that WCW had "no idea" what to do with Hart, which McMahon said was "fortunate for me, in terms of my company; unfortunate for Bret personally." Hart himself has expressed the opinion that he was "poorly used" by the company.On the July 20 edition of Nitro, Hart defeated Diamond Dallas Page for the vacant WCW United States Heavyweight Championship, his first championship in WCW. Hart would go on to hold the United States Heavyweight Championship four times—the most reigns in WCW history. Though still not officially a member of the nWo, the faction did support him in the match, as The Giant came out to the ring and chokeslammed Page. A few days later, Hart lost the United States Heavyweight Championship to fellow WWF alumnus Lex Luger. Hart regained the title from Luger, the next night on Thunder. At Fall Brawl, Hart and several other wrestlers lost to Diamond Dallas Page in a WarGames match. During the fall of 1998 Hart also had an intense feud with Sting which ended at Halloween Havoc with Hart controversially defending the title and (kayfabe) injuring Sting. On the October 26 edition of Nitro, Hart lost the United States Heavyweight Championship to Diamond Dallas Page. The two had a rematch at World War 3 for the title which Hart lost. Hart regained the title from Page on the November 30 edition of Nitro in a No Disqualification match with help from nWo member The Giant.On the February 8 edition of Nitro, Hart lost the United States Heavyweight Championship to family friend Roddy Piper. On the March 29, 1999 edition of Nitro held at Toronto's Air Canada Center, Hart appeared in street clothes and called out Bill Goldberg, verbally coercing Goldberg into tackling him. Hart was wearing a metal breastplate under his Toronto Maple Leafs sweater, which resulted in Goldberg being knocked out. Hart then counted his own pinfall over Goldberg's unconscious body, although there was no match taking place, and left. The incident caused Hart to leave WCW for a short time. When Hart was about ready to return to WCW, his brother Owen Hart died in an accident during a WWF pay-per-view. As a result Hart took time off from WCW to be with his family.
Bret Hart returned to wrestling on the September 13, 1999 edition of Nitro in a match with Hulk Hogan against Sting and Lex Luger. On the October 4, 1999 edition of Nitro he wrestled in a tribute match for Owen against Chris Benoit—this match took place in Kemper Arena in Kansas City, where Owen had died months earlier. Around this same time, the WWF's top writer Vince Russo "jumped ship" to join WCW. Russo instigated an angle which involved a controversy over a series of World Heavyweight Championship matches between Sting, Hogan, and Goldberg at Halloween Havoc, ultimately leading to the title being declared vacant. A tournament then took place over several episodes of Nitro. Hart's first round match came against United States Champion Goldberg, with the match being both for a berth in the next round of the tournament and for the U.S. Title. Thanks to outside interference, Hart was able to defeat Goldberg, handing him his second official WCW loss and winning his fourth U.S. Championship.
On the November 8 edition of Nitro, Hart lost the United States Heavyweight Championship to Scott Hall in a ladder match which also involved Sid Vicious and Goldberg. Hart went on to win the WCW World Heavyweight Championship tournament by defeating Perry Saturn, Billy Kidman, Sting, and Chris Benoit, giving him his first of two reigns in WCW and his sixth world title overall. On December 7, Hart and Goldberg won the WCW World Tag Team Championship from Creative Control but lost the titles to The Outsiders on the December 13 edition of Nitro. At Starrcade, Hart defended his WCW World Heavyweight Championship against Goldberg. During the match, Hart was struck with a mule kick to the head, resulting in a severe concussion. Hart later speculated that he may have suffered up to three additional concussions within matches over the course of that day along with the days immediately following Starrcade, having been unaware of the severity of his injuries. As a part of this, Hart placed Goldberg on the post in a figure-four leg lock which ended with Hart hitting his head on the concrete floor when Goldberg failed to receive the move correctly. The sum total of those injuries left Hart with post-concussion syndrome and ultimately forced his retirement from professional wrestling. Hart wrote a Calgary Sun column in which he said that Goldberg "had a tendency to injure everyone he worked with." As part of his DVD documentary, Hart expressed regret that "someone as good-hearted as Bill Goldberg" was responsible for hurting him.
Hart vacated the WCW World Heavyweight Championship on the December 20 edition of Nitro as a result of controversies surrounding his Starrcade match, offering Goldberg a rematch for the title that evening. Hart defeated Goldberg to regain the title with interference from Jeff Jarrett, Scott Steiner, Kevin Nash, Scott Hall, and Harris Brothers, thus marking the nWo reformation, billed as NWO 2000. Overall, Hart was 3-0 against Goldberg, who was noted for his undefeated streak. He successfully defended the WCW World Heavyweight Championship against Terry Funk and Kevin Nash in January 2000, before vacating the title in late January 2000 when he was forced to withdraw from the main event of WCW's Souled Out due to his injuries. Hart never lost either WCW World Heavyweight Championship he held, but forfeited them instead. Hart continued to make sporadic appearances on WCW television, generally cutting promos, although he did compete in the 41-man battle royal on the May 3, 2000 edition of Thunder. His final WCW appearance occurred on the September 6, 2000 edition of Thunder, in a promo where he confronted Bill Goldberg on the injury he sustained nine months prior. Hart was granted a release from his WCW contract in late 2000 and announced his retirement soon afterward.