Hart signed with the World Wrestling Federation (WWF) in the summer of 1988. Instead of promoting Owen as Bret Hart's younger brother, the WWF decided to create a masked "superhero" type gimmick for him which played to his high-flying style. He broke into the WWF as The Blue Blazer (initially The Blue Angel), with his early appearances seeing him defeat the likes of Terry Gibbs, Steve Lombardi and Barry Horowitz. The Blue Blazer made his pay-per- view debut at Survivor Series, teaming with The Ultimate Warrior, Brutus Beefcake, Jim Brunzell and Sam Houston against The Honky Tonk Man, Greg Valentine, Outlaw Ron Bass, Bad News Brown and Dangerous Danny Davis. The Blazer was eliminated by Valentine, but his team went on to win the match. He continued to wrestle in the midcard, defeating enhancement talent but often falling short against other name talent; he lost to Ted DiBiase on the March 11, 1989 Saturday Night's Main Event XX and was defeated by Mr. Perfect at WrestleMania V.
Hart debuted in World Championship Wrestling's self-titled television show on March 16, 1991, the first of five television matches he competed in, all of which were against preliminary talent such as Mark Kyle. One of the bouts saw him team with Ricky Morton.
Hart signed with the WWF for a second time in 1991. In the WWF, the popular Hart Foundation, composed of his brother Bret and brother-in-law Jim Neidhart, had split up; Bret set out on a singles career while Neidhart was used sparingly. When Neidhart returned from a storyline injury, he joined Owen to form a team known as The New Foundation.
Owen and Neidhart first feuded with the Beverly Brothers. They then had their only pay-per-view match at the Royal Rumble in January 1992, where they beat The Orient Express. Neidhart left the WWF shortly afterward, and Hart set out on a very short run as a singles wrestler, including a match at WrestleMania VIII against Skinner. Shortly after WrestleMania, Hart was teamed up with Koko B. Ware to form the duo known as High Energy. They had only one pay-per-view match as a team, at the Survivor Series, where they lost to The Headshrinkers. The team was quietly dropped at the start of 1993 with Hart starting a singles career. Owen suffered a knee injury on March 9, 1993, in a match taped for Superstars, against Bam Bam Bigelow, which kept him sidelined for nearly two months.
Hart returned to the WWF ring in the fall of 1993, at a time when Bret's feud with Jerry Lawler was temporarily sidetracked. Bret, along with Owen and their brothers Bruce and Keith, were scheduled to face Lawler and his team at Survivor Series. However, Lawler was unable to make it to the show, and as a result could not appear on WWF television. Lawler was replaced with Shawn Michaels. During the match, Owen and Bret inadvertently crashed into each other, causing Owen to be eliminated from the team. Owen showed up after the match and had a heated confrontation with Bret, while Keith, Bruce and their father Stu tried to calm things down. This confrontation resulted in Owen leaving the ring to boos while his brothers and father watched in dismay and mother Helen cried at ringside. The following night, Owen adopted the pink and black tights, sunglasses and Sharpshooter finisher to send a message to his brother. Owen, angry with being in Bret's shadow, challenged his brother, which Bret declined. Instead the brothers seemed to reunite by the holidays.
Bret tried to make amends with Owen, teaming with him on a regular basis. Bret even secured the two a shot at the WWF Tag Team Championship. They faced the Quebecers for the title at the Royal Rumble in January 1994. Initially, everything was fine between the brothers, but when Bret hurt his knee and was unable to tag Owen in for a long period of time, the younger Hart got frustrated. When the referee stopped the match due to Bret's damaged knee, Owen snapped; he kicked his brother in the knee and then walked off, berating Bret on the titantron shortly after as Bret was being helped backstage; this started his run as a heel. After the act, an infuriated Owen accused his brother of being selfish and holding him down. Owen admitted that it felt good to take out his brother. The two brothers faced off for the first time at WrestleMania X, where Owen cleanly pinned his older brother. Later in the evening, Bret won the WWF World Heavyweight Championship while Owen stood by and watched in jealousy as Bret celebrated in the ring. Owen won the 1994 King of the Ring tournament, turning back Razor Ramon in the finals with an elbow drop to the back and with an assist from Jim Neidhart. After the victory, Owen took the nickname "The King of Harts."
Owen and Bret feuded throughout the summer of 1994, clashing many times both in singles and later in tag team matches (with Bret joined by the returning British Bulldog). Two prominent matches took place in this feud: first, their steel cage match in the co-main event of SummerSlam for Bret's WWF World Heavyweight Championship, which Bret won. The second was a lumberjack match on August 17 that Owen initially won and was announced as WWF World Heavyweight Champion; Bret won the match after it was ordered to continue due to interference. At the Survivor Series, Owen struck the most damaging blow against his brother as he conned his own mother Helen to throw in the towel for Bret. The ploy cost Bret the world title to Bob Backlund. Owen also prevented Bret from regaining the title at the Royal Rumble in 1995 when he interfered in the match between Bret and new champion Diesel. In the weeks after the Rumble, Bret and Owen clashed again with Bret soundly defeating his brother, thus putting an end to their feud for the time being.
Owen rebounded from the loss to Bret by winning the WWF Tag Team Championship from The Smoking Gunns at WrestleMania XI. Owen, who was joined by a "Mystery Partner", had challenged the Gunns to a title match; the partner turned out to be former world champion Yokozuna. After the victory, Owen took Jim Cornette and Mr. Fuji as his managers, who already managed Yokozuna. The team defended the title for five months until they lost them to Shawn Michaels and Diesel at In Your House 3. They would briefly hold the titles a second time when the belts were handed back to them before the Smoking Gunns regained the titles. Owen and Yokozuna would continue to team off and on until the end of the year.
In 1995, Owen's brother-in-law Davey Boy Smith turned heel and joined the Camp Cornette stable. During the summer of 1996, the two brothers-in-law started to team up more and more, sometimes alongside Vader, who was also a member of Camp Cornette. Owen was also a color commentator for the 1996 King of the Ring, (exhibiting clear partisan support for Vader and Smith) and during this time wore a cast on his right forearm for several months, feigning a nagging injury to subsequently use his cast as a weapon during his matches.
In September 1996, Bulldog and Hart earned a pay-per-view shot at the Tag Team Titles at In Your House 10. Owen and Bulldog left with the gold after defeating the Smoking Gunns. They also left with a new manager as Clarence Mason had conned Jim Cornette into signing over the contracts of the new champions. Signs of dissension, however, slowly started to show. One occasion where this was evident was at the Royal Rumble, when Hart accidentally eliminated Bulldog. After the Rumble, they had miscommunication in matches against Doug Furnas and Phil LaFon and Bulldog fired Mason after losing a match to Crush, who was also managed by Mason, something which did not sit well with Hart. Another bone of contention between the two was the newly created WWF European Championship; both men had fought their way to the finals to crown the first champion with Bulldog coming out as the victor.
After retaining the Tag Team Titles against the Headbangers by disqualification on the March 24, 1997 edition of Monday Night Raw, the tension between the two bubbled over. An incensed Hart demanded a shot at Bulldog's European Title the next week. The match was booked for March 31; on the night, the two went at it with such intensity that many thought the champions had finally gone their separate ways. Then. in a shocking moment, the recently turned heel Bret Hart appeared at ringside and stopped the match. Bret appealed to both Owen and Bulldog, talking about the importance of family. They agreed to put their differences aside and join with Bret to form the new Hart Foundation, an anti-American stable that also included Hart in-law Jim Neidhart and Hart family friend Brian Pillman.
After forming the Hart Foundation, Owen quickly gained singles gold of his own as he pinned Rocky Maivia to win his first WWF Intercontinental Championship. This meant that the Hart Foundation held every WWF title except the World Title, cementing their dominance over the federation. It was not all success for Owen, though, as he and the British Bulldog lost their tag team title to Stone Cold Steve Austin and Shawn Michaels on May 26, 1997. He began feuding with Austin shortly thereafter.
Owen and Bulldog got a second chance at regaining the tag titles after Michaels vacated his half of the championship due to an injury. On theJuly 14, 1997 edition of Raw, the two entered a tournament and won to face Austin and a partner of his choice that evening for the vacant titles. That partner turned out to be Dude Love, who declared himself to be Austin's partner and helped him defeat Hart and Bulldog for the tag team championships.
At SummerSlam in August, Hart was to defend his Intercontinental Championship against Austin in a "Kiss My Ass" match, where Hart put the title up against Austin having to kiss his buttocks if he lost. During the match, Hart botched a piledriver and dropped Austin on the top of his head, injuring his neck. Austin won the title from Hart that evening, but due to the injury was forced to vacate the title. Although the entire situation was an accident, the WWF decided to make it part of the storyline as Owen began wearing a T-shirt patterned after Austin's that read "Owen 3:16/I Just Broke Your Neck". Hart was then entered into a tournament to crown a new champion.
Hart fought his way to the finals of the tournament to crown the next Intercontinental Champion and was set to face Faarooq at Badd Blood: In Your House. Owen beat Faarooq with Austin's help. Afterward, Austin explained that he wanted to beat Hart for the title when he returned and would not allow Faarooq or anyone else to beat him. After Hart retained the title twice by disqualification between Bad Blood and Survivor Series in Montreal, Austin got his wish and defeated Hart for the Intercontinental Championship again. Later that night, the Montreal Screwjob took place. Bret left the Federation after the event and both the British Bulldog and Jim Neidhart were granted quick releases from their contracts to jump to WCW. This left Owen as the only Hart family member remaining in the WWF, due to his contractual obligations.
Hart was not seen or mentioned on WWF programming until he made a surprise appearance after Shawn Michaels retained his title following a disqualification loss to Ken Shamrock at In Your House: D-Generation X, where he attacked Shawn Michaels. Now a fan favorite, but with a new edgy, antisocial attitude, Hart became known as "The Lone Hart" and also "The Black Hart". Owen had a feud with DX and challenged Shawn Michaels for the WWF World Heavyweight Championship on the December 29, 1997 episode of Raw is War: Hart had Michaels locked in the Sharpshooter when Triple H interfered in order to save Michaels' title, giving Hart the victory by disqualification. He later won the European Title from Triple H, although not directly. Goldust dressed up as Triple H in an attempt to swerve Hart, but Commissioner Slaughter considered him to be a legitimate replacement. Hart later suffered an ankle injury during a match against Barry Windham involving Triple H. When Hart joined the commentary at ringside, Triple H managed to draw Owen into an impromptu title match and regained the title. Chyna interfered while the referee wasn't looking and while Triple H was distracting the referee, she struck Hart behind the left knee with a baseball bat, picked him up and threw him back into the ring where Triple H put Hart in a reverse ankle lock to his injured right ankle to win the European Championship under referees discretion in controversial fashion.
Four weeks after WrestleMania XIV, during a tag team match with Ken Shamrock against Mark Henry and Rocky Maivia, Hart turned on Shamrock, "snapping" his ankle and "biting his ear" in the process. After the attack on Shamrock, Hart became the co-leader, with The Rock, of the Nation of Domination, claiming that "Enough is enough and it's time for a change". The Nation's first big feud after Hart joined was against DX. It was during this feud that D-Generation X parodied the Nation of Domination. The imitation was complete with an actor dressing up as Hart and uttering the phrase "I am not a nugget". Hart's participation in the DX feud was sidetracked when Shamrock returned from injuries dead set on getting revenge on Hart. The two split a pair of specialty matches on pay-per-view, but nothing was ever conclusively settled between them.
Hart remained with the Nation throughout the year until the stable slowly dissolved. After SummerSlam, he teamed with Jeff Jarrett. Hart and Jarrett had Jarrett's manager Debra in their corner.
After a match in which Hart "accidentally injured" Dan Severn, Hart seemingly quit the WWF. Playing off the legitimate injury Hart had inflicted on Austin the year before, the angle blurred the lines between reality and "storyline". Yet as soon as Hart "quit", the Blue Blazer appeared in the WWF claiming to in no way be Hart despite it being very obvious who was under the mask. Unlike the first run of the character, the Blazer was now an overbearing, self-righteous heel who treated the edgy Attitude Era WWF with disdain. Hart and Jarrett ended up making the storyline comical. To prove that Hart was not the Blazer, he showed up beside the Blue Blazer, who was a masked Jarrett. In a later attempt to prove that neither Hart or Jarrett was the Blazer, they both appeared next to a man in the Blue Blazer mask; however, it was obvious that a black man was under the mask. On January 25, 1999, in the midst of the Blue Blazer angle, Hart and Jarrett defeated Ken Shamrock and The Big Boss Man for the Tag Team Titles. The pair successfully defended the belts against Test and D'Lo Brown at WrestleMania XV. They lost the titles to the team of Kane and X-Pac on the (pre-taped) episode of Raw that aired on April 5, 1999. However, Hart and Jarrett continued to team together until Hart's death in May during the Over the Edge pay-per-view event.
On May 23, 1999, Hart fell to his death in Kansas City, Missouri during the Over the Edge pay-per-view event. Hart was in the process of being lowered via harness and grapple line into the ring from the rafters for a booked Intercontinental Championship match against The Godfather. In keeping with the Blazer's new "buffoonish superhero" character, he was to begin a dramatic entrance, being lowered to just above ring level, at which time he would act "entangled", then release himself from the safety harness and fall flat on his face for comedic effect—this necessitated the use of a quick release mechanism. It was an elaboration on a Blue Blazer stunt done previously on the Sunday Night Heat before Survivor Series in 1998. While being lowered into the ring, Hart fell 78 feet, landing chest-first on the top rope (approximately a foot from the nearest turnbuckle), throwing him into the ring.