Smith, along with his tag team partner the Dynamite Kid (known as the British Bulldogs), as well as brothers-in-law Bret Hart and Jim Neidhart were brought in to the World Wrestling Federation (WWF) in 1984. While in the WWF, the Bulldogs began a long running feud with Hart and Neidhart, who were known as The Hart Foundation.
The Bulldogs also feuded with the Dream Team (Greg Valentine and Brutus Beefcake). At WrestleMania 2, with Lou Albano and Ozzy Osbourne in their corner, the Bulldogs defeated the Dream Team for the Tag Team Championship. The Bulldogs held the titles for nearly nine months, feuding with the Dream Team and Nikolai Volkoff and The Iron Sheik. On the 26 January 1987 episode of Superstars, the Bulldogs lost the titles to the Hart Foundation due to a severe back injury to the Dynamite Kid.
After losing the titles, the Bulldogs gained a mascot, an actual bulldog who went by the name Matilda, and feuded with the likes of The Islanders (who in kayfabe dog-napped Matilda), Demolition, and the Rougeau Brothers. The Bulldogs left the WWF in 1988.
Smith returned to the WWF in 1990, where he was pushed as the same character from the British Bulldogs' original WWF run, but this time as a singles star under the name The British Bulldog. Smith returned to the WWF at a live event on 6 October, where he defeated Haku. Smith made his televised in-ring return on 27 October episode of Superstars, where he defeated the Brooklyn Brawler. Over the next two years, Smith was a mid-carder, feuding with the likes of The Warlord and Mr. Perfect.
Smith was a fairly popular wrestler in the United States, but was a huge attraction to fans in the United Kingdom, due to the promotion touring the country holding supercards such as UK Rampage which saw Smith defeat The Berzerker at the London Arena in March 1991 and the Battle Royal at the Albert Hall in which Smith won a 20-man battle royal by eliminating Typhoon on 3 October 1991. After entering as the first man in the 1992 Royal Rumble, he eliminated Ted DiBiase, Jerry Sags and Haku before being eliminated by Ric Flair.
Smith again headlined the WWF's European tours at European Rampage again winning a 15-man battle royal by eliminating The Mountie in München, Germany on 14 April 1992 and defeated Irwin R. Schyster in Sheffield, England on 19 April 1992.
In 1992, due to Smith's newfound popularity in the United Kingdom, the WWF decided to hold its annual SummerSlam pay-per-view in Wembley Stadium in London. The show was main-evented by Smith (led to the ring by the then boxing champion Lennox Lewis) and Bret Hart in a match for Hart's Intercontinental Championship. On 29 August at SummerSlam, in front of 80,355 of his homeland fans, Smith won the title. Smith lost the title to Shawn Michaels on 14 November Saturday Night's Main Event XXXI and was later released by the WWF.
Smith had a stint with World Championship Wrestling (WCW) in 1993 as a face, forming an alliance with top protagonist Sting, and engaging in feuds with top antagonists Sid Vicious and Big Van Vader. Smith wrestled World Heavyweight Champion Vader, on a number of occasions including the main events at Slamboree and Clash of the Champions XXIV. The feud culminated when Smith seemingly won the WCW World Heavyweight Championship from Vader on a tour of England in October 1993, though the decision was reversed. WCW released Smith from his contract in December 1993. His final pay-per-view appearance for WCW during this period came at the November 1993 Battlebowl pay-per-view, where he was teamed with Kole in the first round of the Lethal Lottery; they lost to Road Warrior Hawk and Rip Rogers.
Smith returned to the WWF at SummerSlam in 1994, where he immediately became involved in an ongoing family feud between Bret Hart and his brother, Owen Hart. Smith then teamed up with Bret against Owen and Jim Neidhart in a series of tag team matches, most notably in a victory on Monday Night Raw.
Smith appeared at Survivor Series in a 10-man elimination match. His partners were Intercontinental Champion Razor Ramon, 1-2-3 Kid, and The Headshrinkers. They faced Tag Team Champions Shawn Michaels and Diesel, Owen Hart, Jeff Jarrett, and Jim Neidhart. Smith was eventually counted out.
Smith again played a key part in the main event featuring his brothers-in-law Bret and Owen Hart, in which he supported Bret against Owen's benefactor; Bob Backlund. Smith would be knocked unconscious by Owen, allowing Owen to take advantage of his brother's situation. Owen manipulated Bret's mother to surrender to Backlund on Bret's behalf, thus costing Bret to lose the match and the world title. Two days later, Smith would win a title match against Backlund by countout, just 1 day before Backlund would lose the title to Kevin Nash.
After entering the Royal Rumble as the second entrant in 1995, Smith and Shawn Michaels were the final two remaining participants at the end. Smith tossed Michaels over the ropes and celebrated on the second turnbuckle. However, only one of Michaels feet hit the floor and he was able to reenter the ring and eliminate Smith from behind. Soon after, Smith began teaming with Lex Luger as the Allied Powers. The team wasn't much of a success and only wrestled on two pay-per-views as a tag team. The first came at WrestleMania XI where they defeated The Blu Brothers. The second came at In Your House 2 where they failed to win the Tag Team Championship from Owen Hart and Yokozuna. Afterward the team briefly began feuding with Men on a Mission. On an August episode of Monday Night Raw, the Allied Powers were supposed to face Men on a Mission but Luger (kayfabe) no-showed the match; Smith found a replacement in the WWF Champion Diesel. During the match Smith unexpectedly attacked Diesel and turned heel for the first time in his WWF career, helping Men on a Mission beat up Diesel and aligning himself with Jim Cornette's stable with Owen Hart and Yokozuna, who had been his adversaries just a month earlier, thus disbanding the Allied Powers.
At In Your House 4 in Winnipeg, Manitoba, Smith received a world title shot against Diesel. Smith won by disqualification after Bret Hart interfered. At the Survivor Series in Landover, Maryland, Smith participated in the Wild Card eight-man elimination match. He teamed with Shawn Michaels, Ahmed Johnson, and Sycho Sid. They faced WWF Intercontinental Champion Razor Ramon, Dean Douglas, Owen Hart, and Yokozuna. Smith, Michaels, and Johnson were the survivors.
In December, at In Your House 5 from Hershey, Pennsylvania, Smith was granted a title shot against new WWF Champion Bret Hart in a rematch from their SummerSlam 1992 match. They had another critically acclaimed match yet Hart won this time. A notable incident from this match was that Hart bled during the match, which was controversial because WWF outlawed bleeding at the time.
Smith then entered the 1996 Royal Rumble, where he made it to the final four before being eliminated by Shawn Michaels. At In Your House 6, he lost to Yokozuna by disqualification after Vader interfered. At WrestleMania XII he teamed with Vader and Owen Hart to defeat Yokozuna, Ahmed Johnson, and Jake Roberts. At In Your House 7 in April, Smith and Owen Hart defeated Johnson and Roberts after Smith forced Roberts to submit.
In 1996, after Shawn Michaels became world champion, Smith was put in a feud with the new champion. The feud was supposedly based on Smith's wife, Diana, accusing Michaels of hitting on her, which angered Smith and made him determined to take the title from Michaels. The two main-evented the In Your House 8: Beware of Dog pay-per-view, and their match ended in a draw, leading to a rematch at the 1996 King of the Ring pay-per-view. Michaels ended up successfully defending the title.
Afterwards, Smith formed a tag team with his brother-in-law, Owen Hart, and the two soon won the World Tag Team Titles from The Smokin' Gunns. The team defended their titles against teams such as Doug Furnas and Phil LaFon, Vader and Mankind, and The Legion of Doom.
In 1997, the WWF created the WWF European Championship, and Smith became the first ever holder of the title, winning a tournament which culminated in him defeating his own tag team partner, Owen Hart, in the finals on 26 February.
Hart and Smith later joined forces with Bret Hart, Jim Neidhart, and Brian Pillman to form a new form of the Hart Foundation, a heel faction which feuded with Stone Cold Steve Austin and other American wrestlers. This created an interesting rift between American fans, where the Hart Foundation were vilified, and Canadian fans, who revered the Hart Foundation. Smith and Owen dropped the World Tag Team Titles to Austin and Michaels, and lost the final match in a tournament for the vacant Tag Team Titles to Austin and Dude Love. Smith then started a feud with Ken Shamrock for the European Title, and eventually lost the European Title to Shawn Michaels at the British pay-per-view event One Night Only. Smith was booked in the main event to defend the belt against Michaels. This marks the only time Smith lost on a WWF card in the United Kingdom. On 9 November at Survivor Series in Montreal, Smith was part of Team Canada (alongside Jim Neidhart, Doug Furnas and Philip Lafon), defeating Team USA (Vader, Goldust, Marc Mero and the debuting Steve Blackman). The event became infamous for the "Montreal Screwjob", in which Vince McMahon manipulated the finish of Bret Hart's match and had him lose the WWF Championship to Michaels, despite Hart not submitting when placed in a Sharpshooter. Smith left the WWF for WCW, along with Bret Hart and Neidhart, soon afterward.
Smith rejoined WCW in late 1997, and began a feud with Steve McMichael, who was complaining about all the wrestlers coming from "Up North". Smith and Neidhart later formed a tag team, but were only featured sparingly on WCW Thunder. They challenged for the World Tag Team Championship on several occasions, but failed to win the titles.
Smith suffered a knee injury in April 1998 that sidelined him for a month. He suffered another, much more serious injury on 13 September 1998 at Fall Brawl during his match with Neidhart against The Dancing Fools, Disco Inferno and Alex Wright. During the match, while taking bumps, Smith twice landed awkwardly on a trapdoor that had been set up underneath the ring canvas to enable The Warrior to make a dramatic entrance in the night's main event. Smith was released soon after.
Smith returned to the WWF in September 1999, following the death of Owen Hart in an in-ring accident. In keeping with the company's new "Attitude Era", Smith began wrestling in jeans instead of his usual Union Flag-adorned tights and his theme music was changed from "Rule, Britannia!" to a remix of that particular theme, and later to generic rock music (complete with the sounds of a dog barking as the song began) that WWF used for most of its talent at the time. On the 7 September episode of SmackDown! in Albany, New York, Smith defeated the Big Boss Man for the WWF Hardcore Championship. Smith forfeited the title later that evening, giving the belt back to Al Snow, because Boss Man had previously (kayfabe) dog-napped Snow's dog Pepper to win the title from him, and driving him insane in the process. Smith then began pursuing the WWF Championship, eventually turning heel and beginning a feud with The Rock. Smith headlined Unforgiven as part of a six-man WWF Championship Match that was won by Triple H. On 2 October, Smith returned to England as a heel at Rebellion. He then lost to The Rock at No Mercy.
Smith defeated D'Lo Brown for the WWF European Championship on SmackDown! on 26 October. He lost the title to Val Venis in a triple threat match at Armageddon.
On 6 May 2000 in London, Smith defeated Crash Holly for the Hardcore Championship. Holly regained the title from Smith in New Haven, Connecticut on the 11 May episode of SmackDown!. Smith's last televised match with the WWF was on Sunday Night Heat some weeks later, when he burst into Eddie Guerrero and Chyna's locker room, accusing Guerrero (who was the European Champion at the time) of not treating the belt with the respect it deserved. This led to a title match on Heat, in which both men were disqualified. After Heat, WWF announced that Smith had again left the WWF on 15 May 2000.
Smith passed away on May 18, 2002.
In 2020, Smith was announced to be posthumously inducted into the WWE Hall of Fame by his son, David Hart Smith.