Steiner debuted in World Championship Wrestling (WCW) during a backstage interview at Chi-Town Rumble on February 20, 1989, later accompanying his brother Rick to the ring as he lost the WCW World Television Championship to Mike Rotunda. Scott would begin wrestling in singles bouts on WCW programming before the Steiners began teaming together. The Steiners lost their first high-profile bout to Kevin Sullivan and Rotunda at Clash of the Champions VII, but defeated them in a rematch at the Great American Bash 1989. The Steiners also competed in the "King of the Hill" two-ring battle royal earlier in the show, but were unsuccessful.
During this time, the Steiners were managed by Missy Hyatt and often brought their pitbull Arnold to the ring. Rick nervously began a relationship with a shy fan named "Robin Green" who eventually received a make-over and transformed into Woman. Green was responsible for tripping up Scott at Clash of the Champions VIII, and costing the Steiners the WCW World Tag Team Championship as well as luring Scott into a parking lot assault by Sullivan and her new masked tag team, Doom. Doom, with Woman in their corner, would defeat the Steiners at Halloween Havoc '89 after Woman interfered.
On November 1, 1989, in Atlanta, Georgia, The Steiner Brothers defeated The Fabulous Freebirds (Michael Hayes and Jimmy Garvin) for the WCW World Tag Team Championship. They held the titles for over five months before losing it to Doom (Butch Reed and Ron Simmons) in Washington, D.C., at Capital Combat. The Steiner Brothers defeated The Midnight Express (Bobby Eaton and Stan Lane) for the WCW United States Tag Team Championship on August 24, in East Rutherford, New Jersey. The Steiner Brothers competed in a WarGames match at WrestleWar 1991. After winning the WCW World Tag Team Championship on February 18, they vacated the United States Tag Team Championship, on February 20.
In 1990, Steiner began wrestling in singles matches. WCW's weekend shows (Power Hour, Saturday Night, and Main Event), featured the WCW Gauntlet Series, in which a wrestler was selected to face a different top star on each show that weekend, winning $10,000 if they defeated all three. Steiner was the first to successfully "run the gauntlet" from September 21–23, defeating Bobby Eaton, Ric Flair and Arn Anderson. On January 30, 1991, Steiner had a WCW World Heavyweight Championship match against Flair at Clash of the Champions XIV: Dixie Dynamite, which ended in a time limit draw. In late 1992, the Steiners temporarily disbanded when Rick suffered a torn pectoral muscle. Scott then started wrestling single matches, and then later teased a heel turn when he teamed with Marcus Bagwell against Steve Austin and Brian Pillman on an October 10, 1992 episode of WCW WorldWide. During the match, Bagwell was injured when he was attacked by Arn Anderson, and when Steiner went to tag Bagwell, he was unable to. An angry Steiner then kicked Bagwell and slammed him into the ring where he was attacked by Austin and Pillman, who then won the match. Shortly afterwards, he won the WCW World Television Championship on October 17, 1992. Steiner later vacated the title when The Steiner Brothers left WCW.
The Steiner Brothers made their World Wrestling Federation (WWF) television debut with a promo on the December 21, 1992 episode of Prime Time Wrestling. They appeared on the debut episode of Raw on January 11, 1993. Their pay-per-view debut came on January 24, at the 1993 Royal Rumble, where they defeated The Beverly Brothers (Blake and Beau). At WrestleMania IX on April 4, The Steiner Brothers defeated The Headshrinkers (Samu and Fatu).
After WrestleMania, The Steiner Brothers feuded with Money Inc. (Ted DiBiase and Irwin R. Schyster). At King of the Ring on June 13, The Steiner Brothers and The Smokin' Gunns (Billy and Bart) defeated The Headshrinkers and Money Inc. in an eight-man tag match. The following evening in Columbus, Ohio, on the June 14 episode of Raw, The Steiner Brothers defeated Money Inc. for the WWF World Tag Team Championship. Money Inc. regained the title on June 16, at a house show in Rockford, Illinois, and lost it back to The Steiner Brothers at another house show, on June 19, in St. Louis, Missouri. The Steiner Brothers defended the title against The Heavenly Bodies (Tom Prichard and Jimmy Del Ray) at SummerSlam on August 30 in their home state of Michigan and walked away victoriously with a pinfall win.
On the September 13 episode of Raw in New York, New York, The Steiner Brothers defended the titles against The Quebecers (Jacques and Pierre) in a "Province of Quebec Rules" match, wherein the title could change hands via disqualification. The match ended when the manager of The Quebecers, Johnny Polo, threw a hockey stick into the ring and Scott caught it. When the referee saw Scott holding the foreign object, he disqualified The Steiner Brothers and awarded the title to The Quebecers. Scott defeated Pierre in a singles match the following week on Raw. Steiner competed in the elimination match main event of Survivor Series, marking his only headlining WWF pay-per-view appearance. On January 22, 1994, Scott Steiner was the first entrant in the Royal Rumble. After nine minutes, he was eliminated by Diesel. Following this, the Steiner Brothers left the WWF in mid-1994.
On July 28, 1995, The Steiner Brothers debuted in Extreme Championship Wrestling (ECW), in Middletown, New York, defeating Dudley Dudley and Vampire Warrior. On August 4, in Jim Thorpe, Pennsylvania, they defeated Dudley Dudley and 2 Cold Scorpio. They made their ECW Arena debut on August 5, at Wrestlepalooza, teaming with Eddie Guerrero to lose to Scorpio, Dean Malenko, and Cactus Jack. On August 25, in Jim Thorpe, they defeated Scorpio and Malenko, and defeated Scorpio and Chris Benoit the following evening. On August 28, they defeated Dudley Dudley and Dances with Dudley in Kennett Square, Pennsylvania. At Gangstas Paradise on September 16, they teamed with Taz and lost to The Eliminators (John Kronus and Perry Saturn) and Jason. On September 23, in Middletown, they defeated Raven and Stevie Richards. Scott Steiner made his final ECW appearance on October 28, teaming with Taz and losing to The Eliminators.
The Steiner Brothers rejoined WCW in 1996. They won the World Tag Team Championship from Harlem Heat on July 24, but proceeded to lose it back to them just three days later. After the formation of the New World Order (nWo), the Steiner Brothers feuded with The Outsiders, who had won the World Tag Team Championship from Harlem Heat. This feud lasted from 1996 to early 1998. At the same time, the Steiners also feuded with other nWo members like Vicious and Delicious and continued to have matches with Harlem Heat. From late 1997 into early 1998, Steiner underwent noticeable physical changes, such as massively increasing his muscle mass, cutting his signature mullet and growing a goatee. During this period, Steiner began feuding with nWo member Buff Bagwell over who had the better physique. Before long, he began leaving Rick in the ring by himself during tag team matches, or starting the match without ever tagging his brother in.
On February 22, 1998, Steiner joined the nWo at SuperBrawl VIII, by attacking his brother Rick while they were defending the WCW World Tag Team Championship against The Outsiders. The next night, on Nitro, he adopted a new gimmick, dyeing his hair and beard blond and further increasing his muscle mass. Scott then adopted the nicknames "White Thunder", in reference to his bleached hair and goatee and his all-white singlet, and "Superstar". However, he soon discarded both nicknames, and instead proclaimed himself as "Big Poppa Pump". Steiner further altered his attire as he began wearing sunglasses and chain mail headgear as part of his ring entrance outfit. He then began teaming with former rival Buff Bagwell and remained a member of the nWo until the group disbanded in early 1999.
In 1999, Steiner feuded with Goldberg, Diamond Dallas Page, Booker T, and Rey Mysterio, Jr., and won the United States Heavyweight Championship and World Television Championship. In late 1999, he was sidelined with a back injury and stripped of the United States Heavyweight Title. On a December 1999 episode of Nitro, Steiner cut a promo to announce his retirement from professional wrestling due to this injury. Later that evening, he revealed himself to, in fact, be in fine health, turning on and attacking Sid Vicious. He continued to be a top heel into 2000 and joined the reformed nWo.
After the nWo disbanded again, Steiner joined The Millionaire's Club in their feud with Vince Russo and Eric Bischoff's New Blood stable, turning face for a brief time. At Spring Stampede, he competed in a tournament for the United States Championship, defeating The Wall by disqualification when he blinded him, which caused The Wall to accidentally chokeslam the referee through a table instead. He then defeated Mike Awesome by submission with his finisher, the Steiner Recliner, before ultimately winning the tournament after defeating Sting in the finals, albeit due to interference from Sting's previous opponent Vampiro. Steiner would also feud with Tank Abbott and his brother, a now-heel Rick. Steiner would turn heel again on former nWo teammate Kevin Nash at Bash at the Beach by helping Goldberg defeat him in a match where fellow nWo alumnus Scott Hall's contract was on the line, joining the New Blood in the process. On November 26, 2000, at Mayhem, Steiner defeated Booker T to win the World Heavyweight Championship, becoming a Triple Crown Champion in the process. In January 2001, Steiner became the centerpiece of Ric Flair's Magnificent Seven stable. He feuded with Booker T over several months and pay-per-views until losing the World Heavyweight Championship back to him on the final episode of Nitro on March 26, 2001. After WCW was purchased by the WWF, Steiner, unlike many of his colleagues, did not join the WWF.
In October 2002, Steiner signed a three-year contract with World Wrestling Entertainment, and returned to WWE television after an eight-year absence at Survivor Series in Madison Square Garden on November 17. There, Scott Steiner attacked Matt Hardy and Christopher Nowinski after they delivered a promo insulting New York City, establishing him as a face. Over the following weeks, General Managers Eric Bischoff and Stephanie McMahon both courted Steiner, each trying to sign him to their respective brand, Raw or SmackDown!. Bischoff was ultimately successful, after McMahon rejected Steiner's sexual advances.
On Raw in January 2003, Steiner began feuding with World Heavyweight Champion Triple H, and his faction Evolution. They began competing against one another for strength and muscle conditioning leading to world title matches at the Royal Rumble and No Way Out. Steiner won the first match by disqualification after Triple H attacked him with a sledgehammer, but lost the second match at No Way Out via pinfall.
On April 14, Steiner faced off against Nowinski in a debate over the Iraq War. Later that year, Steiner formed a tag team with Test, with Stacy Keibler as their manager. The team lasted several months, and feuded with La Résistance. They broke up after Test turned heel and began misogynistic-ally treating Keibler. On June 15, Steiner defeated Test in a grudge match to win the managerial services of Keibler at Bad Blood, but lost her back to Test in a rematch on the August 18 episode of Raw. At Unforgiven on September 21, Steiner faced Test with Keibler's managerial services again on the line with the extra stipulation that, if Steiner lost, he would become Test's manservant. Steiner lost after Keibler's interference backfired, and the tag team was reunited at Test's behest. After another mistake by Keibler cost the team a match on the September 29 episode of Raw, Steiner belly-to-belly suplexed her, resulting in Steiner turning heel and teaming on better terms with Test as Keibler was forced to remain their reluctant manager. On December 1, Mick Foley fired in storyline Steiner and Test freeing Stacy as their manager. His last WWE match was as a part of the 2004 Royal Rumble, lasting over six minutes before being eliminated by Booker T. Steiner suffered an injury in 2004, sidelining him for two months. While injured, he was released from WWE on August 17, 2004.
On March 28, 2022, Steiner was announced for the WWE Hall of Fame class of 2022 alongside his brother Rick.