Credible began wrestling for the World Wrestling Federation (WWF) as an enhancement talent. His first match was a loss to Lex Luger on the March 1, 1993 episode of Monday Night Raw. He continued to wrestle sporadically in WWF throughout 1993 and 1994. He even scored an upset victory against Irwin R. Schyster on the September 20, 1993 episode of Raw, after a distraction by Razor Ramon. He also worked a few matches as an enhancement talent in World Championship Wrestling (WCW) in 1994.
After spending nearly two years in the WWF as an enhancement talent, he was hired to a full-time contract in late 1994. His Portuguese ethnicity inspired the WWF to give him the soccer player character of Aldo Montoya. He made his televised debut as a fan favorite on the November 14 episode of Monday Night Raw, where he picked up a victory over The Brooklyn Brawler. He was once offered to be a part of the Million Dollar Corporation by Ted DiBiase. He refused and told him to "shove his money in his ear". Montoya made his pay-per-view debut at the 1995 Royal Rumble as a participant in the Royal Rumble match. He lasted thirteen minutes until he was eliminated by eventual winner Shawn Michaels. Montoya suffered his first televised loss against Mantaur on the January 29 episode of Action Zone. On the April 8 episode of Superstars, Credible defeated the Intercontinental Champion Jeff Jarrett in a non-title match, which earned him a title shot against Jarrett for the Intercontinental Championship on the April 22 episode of Superstars, where Jarrett retained the title. Montoya appeared at the first In Your House pay-per-view, where he attempted to prevent Jarrett and The Roadie from attacking Razor Ramon after a handicap match.
He made only one pay-per-view appearance in 1996 at the Royal Rumble, where he participated in the Royal Rumble match, where he lasted only two minutes until he was eliminated by Tatanka. His only highlight of the year was an upset victory against Jerry Lawler on the July 27 episode of Superstars, which he gained by pinning Lawler with Jake Roberts' DDT finishing move. He lost to Lawler in a rematch on the August 5 episode of Monday Night Raw. After the match, Lawler poured Jim Beam whiskey down his throat. Throughout this time, Montoya became more of a lower card wrestler. In 1997, Montoya was sent to Extreme Championship Wrestling as part of a talent exchange between WWF and ECW.
Montoya debuted in ECW as "PG-187" in a loss to Chris Candido on August 21, 1997. He later took on the name "PJ Walker". At As Good as it Gets, his character was repackaged as he shaved his head and switched to a grunge style of dress, and adopted a cocky, sneering, ego-maniacal attitude. He was introduced by Jason Knight, who named him Justin Credible. Credible defeated Jerry Lynn by debuting a new finisher called That's Incredible. He began an undefeated streak which included a notable win over The Great Sasuke on the October 24 episode of Hardcore TV. Credible suffered his first loss in ECW against Mikey Whipwreck in his pay-per-view debut at November to Remember. Credible continued his rivalry with Whipwreck, beating him in televised rematches on Hardcore TV, while losing again at Better Than Ever.
Credible quickly became a rising villain in the company and adopted Nicole Bass as his bodyguard. He began his next major feud with the company's veteran Tommy Dreamer in 1998. Credible defeated Dreamer in a first blood match at February's CyberSlam pay-per-view, but lost to him in a match at Living Dangerously. Credible was attacked by his returning nemesis Mikey Whipwreck after the match. The two resumed their rivalry as Credible defeated Whipwreck at Wrestlepalooza. During this time, Credible began a high-profile feud with Jerry Lynn as he lost to Lynn at It Ain't Seinfeld. Credible defeated Lynn in a two out of three falls match at A Matter of Respect and in a standard one-on-one match at the Heat Wave pay-per-view on August 2.
In the fall of 1998, Credible renewed his feud with Tommy Dreamer. He joined forces with Jack Victory and Rod Price against Dreamer and The Gangstanators (John Kronus and New Jack) in a Philly Street Fight at the UltraClash event, where his team lost. Credible and Victory lost to Dreamer and Jake Roberts in a tag team match at the company's premier pay-per-view event November to Remember. However, he defeated Dreamer in the first-ever Stairway to Hell match at the Guilty as Charged pay-per-view on January 10, 1999, thanks to interference by Terry Funk.
In the midst of his rivalry with Tommy Dreamer, Credible aligned himself with Lance Storm after the duo lost a three-way dance against Dreamer at House Party. Storm and Credible continued to feud with Dreamer until the duo formed a tag team at Crossing the Line called The Impact Players. They proclaimed themselves to be "New Franchise" after Shane Douglas teased his retirement but Douglas instead chose Dreamer as his successor. Impact Players were defeated by Dreamer and Douglas at Living Dangerously on March 21. Credible then lost a match to Douglas at CyberSlam. The feud with Dreamer and Douglas ended when Douglas left the company in mid-1999. Following Douglas' departure, Credible faced Sid Vicious in a match at May's Hardcore Heaven, which ended in a no contest.
Impact Players began dominating the roster in singles and tag team competition and quickly earned main event status by feuding with the company's top wrestlers. They defeated Jerry Lynn and Sabu at the Hostile City Showdown event in June, and they lost to Lynn and Rob Van Dam in the main event of the Heat Wave pay-per-view on July 18. Credible then embarked on a feud with Sabu, which culminated in a match between the two at September's Anarchy Rulz pay-per-view, which Credible won. Impact Players' next feud was with The Sandman and the ECW World Tag Team Champions Tommy Dreamer and Raven. At November to Remember, Impact Players teamed with Rhino against Sandman, Raven and Dreamer in a losing effort.
Impact Players continued their rivalry with Raven and Dreamer as they began pursuing the ECW World Tag Team Championship. On the January 7, 2000 episode of ECW on TNN, Credible defeated Dreamer in the second Stairway to Hell match. Impact Players were booked to win the titles from Raven and Dreamer at Guilty as Charged on January 9, 2000. A month later, Impact Players dropped the titles to Dreamer and Masato Tanaka on the March 3 episode of ECW on TNN. Shortly after, Mike Awesome and Raven won the titles from Dreamer and Tanaka. At Living Dangerously, Impact Players defeated both teams in a three-way dance to regain the World Tag Team Championship.
Credible received the biggest push of his career at the CyberSlam event on April 22, when he and Jason attacked rival Tommy Dreamer and Raven after Dreamer defeated Taz to win the ECW World Heavyweight Championship. He threw down his ECW World Tag Team Championship belt and challenged Dreamer to defend the title against him on the spot to which Dreamer agreed. Credible defeated Dreamer to win the title after Dreamer's valet Francine turned on Dreamer. From this point, Francine became Credible's valet. Credible became a loyal ally of The Network and the top wrestler of the group. Upon winning the World Heavyweight Championship, Credible vacated his half of the World Tag Team Championship and berated his mentor and tag team partner Lance Storm, leading to a rivalry between the two. At the Hardcore Heaven pay-per-view, Credible was scheduled to defend the title against Dreamer and Storm in a three-way dance but he refused to defend the title against anyone except Storm and threatened to throw the World Heavyweight Championship. Credible defended the title against Storm in a singles match, during which he injured Storm's valet Dawn Marie with a That's Incredible. Credible retained the title and was assaulted by Dreamer after the match. Credible successfully defended the title against Dreamer in the third Stairway to Hell match between the duo at Heat Wave.
Credible represented The Network with Rhino in a tournament for the vacant World Tag Team Championship in September. They defeated The Sandman and Chilly Willy in the first round before losing to Dreamer and Jerry Lynn in the quarterfinals. Credible defended his World Heavyweight Championship against Network's Steve Corino on the September 15 ECW on TNN, during which Corino brought Dawn Marie as his valet, who had been injured by Credible at Hardcore Heaven. Credible managed to retain the title but it stirred up problems between Credible and Corino. Credible successfully defended the title against Corino and Jerry Lynn in an elimination match on the September 29 episode of ECW on TNN, before losing the title to Lynn at Anarchy Rulz on October 1 after being hit with his own move That's Incredible, ending his five-month reign at 162 days.
Credible competed against Lynn, Corino and The Sandman for the title in a Double Jeopardy match the following month at November to Remember. Corino and Credible eliminated Sandman and Lynn respectively and then Corino defeated Credible to win the title. Credible faced Corino and Lynn in a three-way dance for the title at Massacre on 34th Street, where Corino retained the title. He received another opportunity for the title against Corino and Sandman in a Tables, Ladders, Chairs and Canes match at the company's final pay-per-view Guilty as Charged, where Sandman won the title. He competed against Sandman in the final match in the history of ECW on January 13, 2001, which he won but offered a rematch, which he lost to Sandman.
With ECW facing imminent bankruptcy, Credible returned to the WWF in February 2001, immediately forming an alliance with X-Pac and assisting him in his pursuit of the Intercontinental Championship. The duo eventually formed a stable with Albert known as X-Factor. X-Pac and Credible tried several times to win the Tag Team Championship, but were unsuccessful. The team split when Credible aligned himself with Paul Heyman's band of ECW insurgents and helped form The Alliance with WCW. Credible remained on the Company's "B" shows, forming a team with Raven, until Team Alliance lost at Survivor Series.
Credible was fired along with the rest of the Alliance roster (in kayfabe) by Vince McMahon until Ric Flair was able to save his job and get him drafted over to the Raw brand.
On the Raw brand, Credible wrestled mostly on Sunday Night Heat and lost many singles matches he was in, but managed to become an eight-time Hardcore Champion. His last match on Raw was a squash match in which he was defeated by Batista. Credible was released on January 20, 2003, with his final televised WWE appearance being a loss to Test on the December 8, 2002 episode of Heat.
Credible interfered at the 2005 ECW One Night Stand match between Lance Storm and Chris Jericho, attacking Jericho with a kendo stick.
Credible was rehired by World Wrestling Entertainment in June 2006. He returned to WWE television at the June 7 WWE vs. ECW Head to Head event as a member of the ECW brand of WWE, taking part in a 20-man battle royal. He made several appearances on ECW on Sci Fi before being released from his WWE contract on September 28, 2006. During this brief run he won two matches, both by disqualification. He also lost to CM Punk in Punk's debut match.