In 1990, Holly began making television appearances in World Championship Wrestling, being utilized primarily as a jobber. His first match came on July 30 in Gainesville, Georgia, when he was defeated via submission by United States Heavyweight Champion Lex Luger. Holly then wrestled in a six-man match in Marietta, Georgia on August 6, teaming with "Powerhouse" Tim Parker and Brad Bratton against Ric Flair, Arn Anderson and Barry Windham. On August 13, Holly faced Flair in a singles match that aired on World Championship Wrestling, losing via submission. After an absence of several months, he made a final appearance at a World Championship Wrestling taping on January 21 teaming with Dave Johnson in an unsuccessful effort against The Freebirds in a match that aired February 9, 1991.
Two months later, Bob Holly made his initial appearance in the World Wrestling Federation (WWF). Again, he was portrayed as a jobber. His sole match was a teaming with Mike Sample in a loss to The Bushwhackers on the March 30 edition of WWF Superstars.
Holly returned to the WWF on January 11, 1994. His initial gimmick was that of a race car driver turned wrestler called Thurman "Sparky" Plugg, which was quietly changed to Bob "Spark Plug" Holly. He competed in the 1994 Royal Rumble match, lasting over 21 minutes.
At the Royal Rumble in January 1995, Holly and the 1-2-3 Kid defeated Bam Bam Bigelow and Tatanka in the finals of a tournament to crown new WWF Tag Team Champions. Their title reign lasted only one day, however, as the next day, on WWF Monday Night Raw, Holly and the Kid lost the tag team title to The Smoking Gunns.
On the May 7, 1995 (taped April 26, 1995) episode of WWF Action Zone, Holly pinned WWF Intercontinental Champion Jeff Jarrett in a title match, but as Jarrett had his foot on the ropes, the decision was overturned and the title vacated. Later on in the show, Jarrett defeated Holly in a rematch for the vacant title after pinning Holly with a roll-up. Holly's title win is not recognized by WWE. Holly then competed in the 1995 King of the Ring tournament, defeating Mantaur to qualify before losing to The Roadie in the quarterfinals. He was then the first WWF pay-per-view opponent of Hunter Hearst Helmsley, losing to him at SummerSlam. At Survivor Series, Holly was a part of the Underdogs team along with Marty Jannetty, Hakushi and Barry Horowitz. They were defeated by the Body Donnas team of Skip, Zip, Rad Radford and The 1-2-3 Kid.
Despite lasting nearly 40 minutes in the 1996 Royal Rumble, Holly made very few television appearances in the WWF throughout 1996 and 1997.
In February 1998, a newly-blonde Holly and Bart Gunn joined forces with Jim Cornette as part of his stable. Holly, renamed "Bombastic Bob", and Gunn, renamed "Bodacious Bart" were known collectively as The New Midnight Express. The New Midnight Express defeated The Headbangers on March 30, 1998. They challenged The New Age Outlaws for the WWF World Tag Team Championship at the King of the Ring pay-per-view, but were unsuccessful.
In mid-1998, Holly competed in the WWF Brawl for All, a 16-man shootfighting tournament. He was eliminated in the first round by the eventual winner, Bart Gunn, who defeated him on points.
In November 1998, Al Snow, Bob Holly and Scorpio united and formed The J.O.B. Squad. During that same month on an edition of Raw, they helped Mankind defeat Ken Shamrock and The Big Boss Man in a triple threat match. In February 1999, Scorpio was released by the WWF while Gillberg was later phased out of storylines and The Blue Meanie allied with Goldust. After dwindling down to only two members, Snow wrestled against himself on an edition of Raw before Holly came down to the ring to prevent Snow from hurting himself, which led to the formal breakup of the J.O.B. Squad. Later that month at St. Valentine's Day Massacre: In Your House, Bob Holly, now renamed Hardcore Holly, defeated Snow for the WWF Hardcore Championship to permanently end the J.O.B. Squad.
Holly dropped the championship to Billy Gunn on the March 15, 1999 edition of Raw is War, but regained the title two weeks later at WrestleMania XV, in a triple threat hardcore match also involving Al Snow. He lost the title to Al Snow at Backlash: In Your House. At King of the Ring 1999, while being interviewed by Terry Taylor, Holly debuted his new catchphrase 'WHO CARES?!' after asking Taylor who in the hell he was.
On the August 16, 1999 edition of Raw, Holly introduced his on-screen "cousin" Crash Holly. They unsuccessfully challenged for the WWF Tag Team Championship at SummerSlam. Though simultaneously arguing over who was the better Holly, they won the WWF Tag Team Championship on the October 18, 1999 edition of Raw is War, by defeating the Rock 'n' Sock Connection, after Triple H interfered. They lost the titles two weeks later to Mankind and Al Snow on the November 4 edition of SmackDown!. The Holly Cousins and Too Cool defeated Edge, Christian and The Hardy Boyz in a traditional four-on-four elimination match at Survivor Series, where Hardcore Holly was the lone survivor.
On the November 18, 1999 edition of SmackDown!, Holly challenged The Big Show for the WWF Championship, but was defeated. In early 2000, Hardcore Holly pursued the Intercontinental Championship, losing a match against Chyna due to interference from Chris Jericho. He then lost a triple threat match against Chyna and Jericho for the championship at the Royal Rumble, which was won by Jericho. He lost two more subsequent matches to Jericho for the title, ending their feud.
After Crash Holly won the Hardcore Championship on February 22, 2000, the cousins began feuding over the title. Holly won the Hardcore Championship in a "hardcore" 13-man battle royal at WrestleMania 2000. He lost the title back to Crash the following night on Raw. He then sporadically challenged for both the Intercontinental and Hardcore Championships the following months. Holly then missed several months of ring time due to a legitimately broken arm, suffered in a match with Kurt Angle on June 29, 2000 edition of SmackDown. After his return, later in 2000, another on-screen cousin, Molly Holly was introduced. Holly returned on the November 13, 2000 edition of Raw is War, where Holly, Crash Holly and The Undertaker defeated Edge and Christian, and Kurt Angle in a six-man tag match. At Survivor Series, Holly faced William Regal for the WWF European Championship but lost by disqualification. Holly received a rematch at the title at Armageddon, but was defeated by Regal. At the 2001 Royal Rumble, Holly competed in the 30-man Royal Rumble match but was eliminated by The Undertaker. In February, Holly won the Hardcore title three more times, but each time re-lost the title moments later under the "24/7 Hardcore rule." Holly competed in the 2001 King of the Ring tournament, but lost to Kurt Angle in the first round.
In early 2002, Holly worked as a trainer for Tough Enough II, a reality television show produced by WWE where participants underwent professional wrestling training and competed for a contract with WWE.
In 2002, Holly turned heel on SmackDown! and began a short feud with Randy Orton. He then had a minor feud with Kurt Angle after eliminating him from a battle royal, turning him face again. Holly suffered a broken neck during a 2002 match against Brock Lesnar, when he was powerbombed neck first on the mat. He had a thirteen-month hiatus from wrestling after surgery. While awaiting surgery, Holly made a guest appearance on Tough Enough III.
Holly returned at the Survivor Series pay-per-view in November 2003 for revenge. He challenged Lesnar to a match for the WWE Championship at the Royal Rumble, but lost. During 2004 and early 2005, he formed short-lived tag teams with Billy Gunn, and later Charlie Haas in the hunt for the Tag Team Championship, but was unsuccessful with both partners. He also failed to claim the WWE Championship from John "Bradshaw" Layfield in a hardcore match.
In mid-2005, Holly went into singles competition trying to acquire the United States Championship from Orlando Jordan. After being defeated twice by Jordan, Holly finally managed to pick up a non-title win over Jordan via disqualification on WWE Velocity, which aired on August 6, 2005. Holly then entered a short feud with SmackDown! newcomer, Mr. Kennedy. This feud climaxed on October 9, 2005 at No Mercy, where Kennedy defeated Holly after a Green Bay Plunge. Holly then underwent several surgeries to repair nagging injuries.
Holly made a surprise appearance at WWE's ECW house show event on August 21, 2006 in Allentown, Pennsylvania, defeating Balls Mahoney. Holly made his ECW television debut the next night, August 22, appearing in a promo with Paul Heyman, and later attacking Rob Van Dam and Danny Doring during a match. Holly, now as a heel, soon joined with Heyman and his other associates to feud with RVD and others.
On September 26, 2006, Holly received 24 stitches in his back after suffering a severe laceration during an Extreme Rules match against Rob Van Dam when he landed on the metal railing of a table he was suplexing Van Dam out of the ring during an ECW show in Tulsa, Oklahoma. Holly obtained the injury early in the match but continued to wrestle until the match's conclusion when he was pinned. The legitimate incident caused fans to cheer Holly in the following weeks, leading him to become a face character and a feud with Paul Heyman's other enforcer Test. His second to latest run as a face was short lived as he eventually turned on Rob Van Dam when they were partners in a tag match.
When Sabu was found unconscious in the locker room area before the Extreme Elimination Chamber at December to Dismember, Holly was chosen as his replacement. Holly entered with Rob Van Dam as the first of two combatants. He was the second to be eliminated; he was eliminated by Test by a running big boot. Subsequently, he entered into a feud with CM Punk whereby Holly, now a tweener, showed his endurance by surviving Punk's Anaconda Vice submission hold. Holly then gave Punk his first loss in ECW; Punk had been undefeated for half a year. After Test replaced Holly in a match against ECW World Champion Bobby Lashley, Holly vowed he would become champion whether he faced Test or Lashley. Holly then was one of ECW superstars entered in the Royal Rumble, but was eliminated by The Great Khali. Holly soon became the number one contender for Lashley's ECW Championship and faced off against Lashley, albeit unsuccessfully.
On April 3, 2007, Holly lost to Snitsky. After the match, Snitsky wedged Holly's arm between the steel steps and repeatedly hit the steps with a steel chair, resulting in a broken arm in the storyline. Holly had surgery on April 16 and missed around five months.
Holly was drafted back to SmackDown! from ECW on June 17, 2007 as part of the supplemental draft. Despite this, he returned to the ring as a member of the Raw brand on September 24, 2007, defeating Cody Rhodes, and starting a "respect" feud in which Holly defeated Rhodes on the two following episodes of Raw. On the October 22 episode of Raw, Holly became a fan favorite by saving Rhodes from the post-match assault of Shelton Benjamin and Charlie Haas. On the October 29 episode of Raw, Holly and Rhodes emerged victorious in a tag team match against Benjamin and Haas. They earned a shot at the World Tag Team Championship by defeating Paul London and Brian Kendrick and The Highlanders in a WWE.com exclusive match after an Alabama Slam. Holly and Rhodes lost their title match, however, against Lance Cade and Trevor Murdoch at Survivor Series.
On December 10, 2007, on the Raw 15th Anniversary episode, Holly along with Rhodes defeated Lance Cade and Trevor Murdoch for the World Tag Team Championship. The following week, Holly and Rhodes retained their title, in their first title defense, against Cade and Murdoch. They successfully defended their title against the teams of Carlito and Santino Marella and Paul London and Brian Kendrick. On June 29 at Night of Champions, Rhodes turned on Holly by defeating him with Ted DiBiase in a handicap match to crown the new team as champions. This was Holly's last WWE appearance. After seven months of inactivity, WWE announced that Holly was released from his WWE contract on January 16, 2009, ending his 15-year tenure with the company.