Jarrett debuted in the World Wrestling Federation (WWF) under the gimmick of "Double J" Jeff Jarrett, a country music singer who intended to elevate his singing career through his exposure as a wrestler. Jarrett's character would strut to the ring wearing flashing "Double J" hats and ring attire, and he punctuated his promos with the phrase "ain't I great?". He ended his interviews by distinctly spelling out his name ("That's J-E-Double-F, J-A-Double-R, E-Double-T!").
Jarrett made his pay-per-view debut in January 1994 at the Royal Rumble. At SummerSlam, he pinned Mabel. At Survivor Series, Jarrett competed in a 10 man elimination tag match. At the 1995 Royal Rumble in Tampa, Florida, Jarrett defeated Razor Ramon to win the WWF Intercontinental Championship. Ramon received a rematch at WrestleMania XI which Jarrett lost by disqualification, but retained the championship. Jarrett was then joined by The Roadie, with the duo losing to Ramon in a handicap match at In Your House 1. On April 26, 1995, the WWF Intercontinental Championship was declared vacant after a controversial ending to a match between Jarrett and Bob Holly. They had a rematch later that evening where Jarrett reclaimed the title. On May 19, Ramon regained the title from Jarrett in Montreal, Quebec, but Jarrett won it back two nights later in Trois-Rivières, Quebec, making him a three time Intercontinental Champion.
At In Your House 2: The Lumberjacks on July 23, 1995, Jarrett and Sawyer Brown performed the song "With My Baby Tonight". Later that evening, Jarrett lost the WWF Intercontinental Championship to Shawn Michaels. Following the event, Jarrett left the WWF for several months and returned to the United States Wrestling Association. Jarrett returned to the WWF in late 1995, feuding with Ahmed Johnson. Jarrett lost to Johnson by disqualification at the 1996 Royal Rumble and left the WWF shortly thereafter due to a contract dispute. Later that year, The Roadie revealed that he had in fact sung "With My Baby Tonight" and that Jarrett had been lip synching.
In October 1996, Jarrett was hired by World Championship Wrestling (WCW), signing a one year contract. Upon debuting in WCW, Jarrett became a "free agent" in the rivalry between the Four Horsemen and the New World Order. After defeating Chris Benoit at Starrcade, Jarrett was inducted into the Four Horsemen. On June 9, 1997, Jarrett defeated Dean Malenko to win the WCW United States Heavyweight Championship. In mid-1997, Jarrett left the Four Horsemen and began feuding with Horsemen member Steve "Mongo" McMichael. Despite aligning himself with McMichael's ex-wife, Debra McMichael, Jarrett lost the WCW United States Heavyweight Championship to McMichael on August 21. In October, Jarrett's contract expired and he opted to return to the World Wrestling Federation, despite the dominance of WCW in the ongoing Monday Night Wars.
Jarrett returned to the WWF on the October 20, 1997 episode of Monday Night Raw, delivering a worked shoot speech in which he criticized both WCW President Eric Bischoff and WWF Chairman Vince McMahon. After briefly feuding with The Undertaker, Jarrett defeated Barry Windham to win the vacant NWA North American Heavyweight Championship. In early 1998, Jarrett joined forces with Jim Cornette and his stable of "invading" National Wrestling Alliance wrestlers, and began defending the NWA North American Heavyweight Championship on WWF television. In March, Jarrett left Cornette's stable, and Cornette stripped him of the title and awarded it to Windham.
Jarrett went on to reprise his country music singer gimmick, introducing Tennessee Lee as his manager and the tag team Southern Justice (formerly known as The Godwinns) as his bodyguards. He redeveloped his habit of breaking an acoustic guitar over the heads of his opponents. At Unforgiven: In Your House, Jarrett once again sang alongside Sawyer Brown. In August, Jarrett abandoned his country singer gimmick and dismissed Lee. He and Southern Justice began feuding with D-Generation X, with Jarrett losing to D-X member X-Pac in a hair versus hair match at SummerSlam. Jarrett's long hair was subsequently cut short by D-X and ring announcer Howard Finkel, who had himself been shaved bald by Jarrett and Southern Justice shortly before SummerSlam. Jarrett and Southern Justice were defeated by D-X at Breakdown in September, and the trio separated shortly thereafter.
Jarrett briefly feuded with Al Snow before reuniting with Debra, who had left WCW for the WWF, and forming a tag team with Owen Hart. Jarrett and Hart won the WWF Tag Team Championship from Ken Shamrock and Big Boss Man, successfully defending the titles at WrestleMania XV before losing to Kane and X-Pac on an episode of Raw. Eight days after Hart was killed in a stunt that went wrong at Over the Edge, Jarrett defeated The Godfather, who Owen was scheduled to face at the pay-per-view. Jarrett use Owen Hart's finisher, the Sharpshooter, to pick up the win. As he was handed the title he yelled Hart's name in tribute to his friend. In mid-1999, Jarrett won and lost the WWF Intercontinental Championship on two more occasions.
In the months that followed, Jarrett became increasingly abusive towards Debra. At SummerSlam, Jarrett challenged D'Lo Brown for both the WWF European and Intercontinental Championships, with Debra accompanying Brown to the ring following an argument with Jarrett. Brown lost the match after both Mark Henry and Debra turned on him, making Jarrett the second ever "Euro-Continental Champion". On the following episode of Raw, Jarrett rewarded Debra and Henry by giving Debra an assistant, Miss Kitty, and Henry the European Championship. In late 1999, Jarrett began feuding with Chyna over the Intercontinental Championship. In the course of the feud, Jarrett became somewhat misogynistic, attacking numerous females, including both wrestlers and actress Cindy Margolis, and executing the figure four leglock on them. Jarrett eventually abandoned Debra in favor of Miss Kitty after he and Debra were defeated by Stephanie McMahon and Test in a mixed tag team match. He later also turned on Miss Kitty after she lost a match that Jarrett had inserted her into in his place.
Jarrett left the WWF in October 1999, right after WWF head writer Vince Russo resigned from the WWF in order to join WCW. Jarrett's contract expired on October 16, 1999, one day before his scheduled match with Chyna at No Mercy. Jarrett wrestled at No Mercy nonetheless, losing the Intercontinental Championship to Chyna. Chyna later alleged that Jarrett and Russo had colluded in order to delay Jarrett's title defense until after Jarrett's contract had expired, and that Jarrett had subsequently blackmailed WWF Chairman Vince McMahon for $300,000 in order to wrestle without a contract. In 2006, Jarrett asserted that he had been paid only what he was owed by the WWF.
Jarrett returned to WCW on the October 18, 1999 episode of WCW Monday Nitro, attacking Buff Bagwell and proclaiming himself the "Chosen One" of WCW. Jarrett took part in a tournament for the vacant WCW World Heavyweight Championship, winning his first three matches with the assistance of Creative Control. At Mayhem, he was eliminated from the tournament after losing his semi-final match to Chris Benoit following interference from Dustin Rhodes. At Starrcade, Jarrett defeated Rhodes in a bunkhouse brawl, then unsuccessfully challenged Benoit for the WCW United States Heavyweight Championship in a ladder match. On the following episode of Monday Nitro, Jarrett defeated Benoit in a rematch. In the same evening, Jarrett reformed the New World Order with Bret Hart, Kevin Nash, and Scott Hall, with the foursome calling themselves "nWo 2000".In early 2000, Jarrett feuded with WCW Commissioner Terry Funk, who forced him to wrestle three veterans - George "The Animal" Steele, Tito Santana, and Jimmy "Superfly" Snuka - in a single night. Jarrett was stripped of the United States Heavyweight Championship after suffering a concussion during his bout with Snuka, but the title was returned to him by Nash after he became WCW Commissioner. In order to help him retain the title, Jarrett drafted the Harris Brothers into nWo 2000. In the following months, Jarrett repeatedly challenged Sid Vicious for the WCW World Heavyweight Championship, in the process clashing with Nash and winning the position of WCW Commissioner for himself. Following the retirement of Hart, the New World Order disbanded.In April, WCW was "rebooted" by Eric Bischoff and Vince Russo, with all titles vacated as a result. Bischoff and Russo also created the New Blood, a stable of younger wrestlers who feuded with the Millionaire's Club, made up of the older members of the WCW roster. Jarrett joined the New Blood, and at Spring Stampede on April 16, he defeated Millionaires Club member Diamond Dallas Page to win the vacant WCW World Heavyweight Championship. Page regained the title on April 24, and on April 25, the title was contested in a tag team match pitting Jarrett and Bischoff against Page and actor David Arquette. Arquette won the WCW World Heavyweight Championship after pinning Bischoff (despite neither of the two being the legal men in the ring—Jarrett hit Page with the championship belt while special referee Kimberly Page's back was turned; WCW official Mickie Jay counted Bischoff out while Jarrett had Page pinned. At Slamboree on May 7, Jarrett defeated Page and Arquette in a three way triple cage match to win his second WCW World Heavyweight Championship after Arquette turned on Page..In May, Jarrett won and lost the World Championship on two further occasions, regaining the title from Ric Flair both times. Jarrett feuded with Nash and Hulk Hogan throughout June 2000, and on July 9 at Bash at the Beach, he faced Hogan with the World Championship on the line. The match ended swiftly after Jarrett immediately laid down, allowing Hogan to rest a boot on his chest and win the title, with Hogan commenting, "That's why this company is in the damn shape it's in—because of bullshit like this." Vince Russo subsequently came to the ring and delivered a profanity-laced interview in which he accused Hogan of politicking and claimed that Hogan had used his creative control to refuse to lose to Jarrett. Russo then stated that, while Hogan was free to keep the title belt he had just won (the "Hulk Hogan Memorial Belt"), Jarrett would wrestle Booker T for the official WCW World Heavyweight Championship later that night. Booker T won the resultant match, and Hogan did not appear in WCW again. It is disputed whether the situation was a shoot, a work, or some combination of the two.In the following months, Jarrett briefly feuded with Booker T, Mike Awesome, Sting, Buff Bagwell, and Flair. In late 2000, he joined forces with the Harris Brothers once more, with the trio defeating the Filthy Animals at Starrcade on December 17. In the same evening, Jarrett aligned himself with WCW World Champion Scott Steiner by helping Steiner defeat Sid Vicious. In 2001, Jarrett and Steiner became members of the Magnificent Seven, a large stable headed by Flair. Flair and Jarrett feuded with Dusty and Dustin Rhodes until March, when WCW was purchased by the WWF. His contract was not picked up by the WWF. On the last Nitro, Jeff was seen on RAW while Vince McMahon watched the show. Vince saw Jeff on the screen and told the viewer that Jarrett would not have a future in the WWF following McMahon's acquisition of WCW, effectively firing him on-air. This was obviously due to the way Jarrett had left the WWF two years earlier.