After the first WWWF World Champion, Nature Boy Buddy Rogers, was hospitalized three times in April of 1963 for chest pains, Vince McMahon, Sr. and Toots Mondt made a command decision to make an emergency title switch. Between Antonino Rocca and Bruno Sammartino, they went with the younger Sammartino who was 28 years old at the time. The match was scheduled to be concluded quickly so as not to risk Buddy's health any further. Sammartino won the title on May 17, 1963, defeating Rogers in 48 seconds. Sammartino and Rogers faced each other two months later at Madison Square Garden in a tag team match, with Rogers and Handsome Johnny Barend defeating Sammartino and Bobo Brazil by 2 falls to 1. Rogers pinned Sammartino for the third and deciding fall. Rogers retired prior to their scheduled title rematch on October 4, 1963, in Jersey City, New Jersey's Roosevelt Stadium. Sammartino instead that night had his first match against new number one contender, Gorilla Monsoon. Because Monsoon won the match by disqualification, thus Sammartino retained his belt.
On December 8, 1969, he teamed with Tony Marino to win the WWWF International Tag Team Championship by defeating The Rising Suns (Tanaka and Mitsu Arakawa). Company policy meant that Sammartino could not hold two championships simultaneously, so he was replaced by Victor Rivera. Sammartino held the WWWF World Heavyweight Championship for seven years, eight months, and one day (2,803 days). On January 18, 1971, Sammartino lost the championship at Madison Square Garden to Ivan Koloff. Later that year, he won the International Tag Team Championship for the second time by teaming with Dominic DeNucci.
Soon after, Sammartino and then-WWWF champion Pedro Morales teamed up for a series of tag team matches. In a televised match, Professor Tanaka blinded both men with salt and they were maneuvered into fighting each other. When their eyes cleared, they kept fighting each other. Two weeks later, all syndicated wrestling shows in the WWWF showed a clip of Sammartino and Morales signing a contract for a title match at Shea Stadium. When McMahon Sr. gestured for them to shake hands, both wordlessly turned and walked away. On September 30, 1972, Sammartino and Morales wrestled to a 65-minute draw at Shea Stadium in New York.
Eventually, on December 10, 1973, Sammartino regained the WWWF Heavyweight Championship by defeating Stan Stasiak. During this time, on April 26, 1976, Sammartino suffered a legitimate neck fracture in a match against Stan Hansen at Madison Square Garden, when Hansen improperly executed a move and dropped Sammartino on his head. After two months, Sammartino returned and faced Hansen in a rematch on June 25, 1976 at Shea Stadium, which was on the closed circuit TV undercard of the Muhammad Ali vs. Antonio Inoki match for WWWF cities.
In early 1977, Sammartino informed McMahon Sr. that he felt he could no longer continue as champion due to his injuries. On April 30, 1977, he was defeated by Superstar Billy Graham for the title. His second title run lasted three years, four months, and twenty days (1,237 days). Despite a very long series of rematches against Graham, Sammartino was unable to regain the title. His final attempt was in Philadelphia, just a few days before Graham was scheduled to lose the title to Bob Backlund.
Following his inability to regain the WWWF title, Sammartino began serving as color commentator for the WWF's syndicated programs, WWF Championship Wrestling and WWF All-Star Wrestling.
On January 22, 1980, his former student Larry Zbyszko turned on him at the World Wrestling Federation's Championship Wrestling show. Sammartino, shocked and hurt by Zbyszko's betrayal, vowed to make Zbyszko pay dearly. Their feud culminated on August 9, 1980, in front of 36,295 fans at Shea Stadium. As the main event of 1980's Showdown at Shea, Sammartino defeated Zbyszko inside a steel cage.
Sammartino retired from wrestling full-time in 1981, in a match that opened the Meadowlands Arena in East Rutherford, New Jersey. Sammartino pinned George "The Animal" Steele in his match.
At the inaugural WrestleMania at a sold out Madison Square Garden in 1985, Sammartino was in his son David's corner for his match against Brutus Beefcake. The match ended in a double-disqualification after the Sammartinos began brawling with Beefcake and his manager Johnny Valiant. He returned to in-ring action soon after with his son, as they wrestled against Beefcake and Valiant at Madison Square Garden. The Sammartinos also teamed against "Mr. Wonderful" Paul Orndorff and Bobby "The Brain" Heenan in various arenas.
Sammartino's highest-profile feud during this run was with "Macho Man" Randy Savage. An irate Sammartino attacked Savage during a TV interview, after Savage bragged about injuring Ricky Steamboat, by driving the timekeeper's bell into Steamboat's throat during a televised match. Sammartino defeated Savage in a lumberjack match for the WWF Intercontinental Heavyweight Championship via disqualification at the Boston Garden. This allowed Savage to keep the championship, as titles cannot change hands via countout or disqualification. He was often teamed with Tito Santana and his old enemy George "The Animal" Steele (who was a fan favorite at this point in his career) to wrestle Savage and "Adorable" Adrian Adonis. The climax of their feud came was a victory for Sammartino and Santana in a steel cage match in Madison Square Garden. Sammartino also engaged in a feud with "Rowdy" Roddy Piper after Piper insulted his heritage on a segment of Piper's Pit at Madison Square Garden. Sammartino faced Piper in both singles and tag team matches. Sammartino teamed with Paul Orndorff in his matches against Piper, while Piper would tag with his "bodyguard", Ace "Cowboy" Bob Orton. Sammartino would eventually get the upper hand in the feud, by defeating Piper in a steel cage match at the Boston Garden. In 1986, Sammartino competed in a 20-man battle royal at WrestleMania 2 at the Rosemont Horizon in Chicago.
Sammartino's final match was at a WWF house show in Baltimore on August 29, 1987, where he teamed up with Hulk Hogan to defeat King Kong Bundy and One Man Gang in the main event. Sammartino continued doing commentary on Superstars of Wrestling until March 1988.
On October 28, 1989, Sammartino made a special appearance at the WCW pay-per-view event Halloween Havoc, where he was the special guest referee in a "Thunderdome" cage match which featured Ric Flair and Sting taking on Terry Funk and The Great Muta. Sammartino worked several WCW events in a minor analysis role in the early 1990s, as well as a brief run doing color commentary with Jim Ross on Saturday Night in 1992. He also acted as special guest referee in World Championship Wrestling (WCW) for a series of matches between Flair and Randy Savage in June 1996.
In 2013, Sammartino accepted an invitation for induction into the WWE Hall of Fame. The ceremony took place at Madison Square Garden on April 6, 2013, and Sammartino was inducted by Arnold Schwarzenegger. Sammartino appeared on the October 7, 2013, episode of Raw and received a birthday greeting in his hometown of Pittsburgh. On March 28, 2015, Sammartino inducted Larry Zbyszko into the WWE Hall of Fame.
On April 18, 2018, Sammartino passed away.