Dykstra made his first national television appearance in WWE at the age of 17 on the May 12, 2003 episode of WWE Raw as Ken Phoenix. Along with his brother, Mike Phoenix, he was a participant in Rodney Mack's ongoing "5-Minute White Boy Challenge" where Mack defeated Caucasian wrestlers in under five minutes. Mack defeated the pair in 1:31, forcing them both to submit to his new Blackout finishing hold. He made another appearance, losing to Lance Storm on an episode of Sunday Night Heat.
On the January 23, 2006, episode of Raw, Dykstra, along with the Spirit Squad, debuted and helped Jonathan Coachman win a Royal Rumble qualifying match against Jerry "The King" Lawler by performing cheers for Coachman and distracting Lawler. They later became a part of the on-going scripted feud between WWE chairman Vince McMahon and Shawn Michaels. The villainous McMahon brought in the Squad to attack Michaels on numerous occasions, including placing them in multiple handicap matches.
They also continued wrestling in the tag team division, and on April 3, on Raw, the Squad won the World Tag Team Championship when Kenny and Mikey, with outside help from the other three Squad members, defeated the team of Big Show and Kane. After winning the championship, all five members of the team were recognized as the champions, allowing any combination of them to defend the championship.
Three weeks later, McMahon scheduled another handicap match, with the Spirit Squad facing Michaels. The match never started, however; instead the Spirit Squad brutally beat down Michaels, ripping apart his ring attire and, as part of the storyline, shattered his knee with a steel chair. McMahon then called Triple H to the ring to attack Michaels with a sledgehammer; however, Kenny snatched the sledgehammer away from him, disrespecting Triple H, which led to him attacking the group. Triple H and Michaels revived their former team, D-Generation X (DX), and began a feud with the Spirit Squad. DX played various sophomoric pranks on the team and the McMahons (Vince and his son Shane), as well as defeating the Spirit Squad in handicap tag team matches at Vengeance and a clean sweep in an elimination handicap match at Saturday Night's Main Event.
At the same time as their feud with DX and their alignment with McMahon, the team also wrestled other teams in Raw's tag division over the World Tag Team Championship. The group successfully defended the tag team championship against the teams of Jim Duggan and Eugene, Charlie Haas and Viscera, and Snitsky and Val Venis. They then entered a lengthy feud with The Highlanders, whom they eventually defeated to retain the title at Unforgiven.
The Squad as a whole later began a losing streak with separate members losing singles matches to Ric Flair on consecutive episodes of Raw. After two consecutive losses to the debuting Cryme Tyme, Kenny attacked Mikey on the October 23 episode of Raw, and announced that he was going to defeat Flair. Kenny was successful, despite Flair attempting to even the odds by bringing other WWE Legends (Dusty Rhodes, Sgt. Slaughter, and "Rowdy" Roddy Piper) to the ring with him. It was then announced that Flair and a legend, selected by interactive voting, would wrestle the team for the World Tag Team Championship at the Cyber Sunday pay-per-view in early November. The fans chose Piper, and he and Flair defeated Kenny and Mikey to win the championship.
The group disbanded on the November 27 Raw after losing a five-on-three match against Flair and DX.
After the breakup of the Spirit Squad, he debuted new attire, new theme music, and a new name; Kenny Dykstra. He became interested in joining the group Rated-RKO, which consisted of Edge and Randy Orton. In order to join, he was told to prove himself first. He continued the feud with Ric Flair that led to the breakup of the Spirit Squad, managing to pick up three straight victories over Flair before finally losing to him. After the feud with Flair, Dykstra become a mainstay on Raw's sister show Heat, having feuds with both Eugene and Val Venis.
He then formed a tag team with Johnny Nitro, but the duo split when Kenny was drafted to the SmackDown! brand on June 17, 2007, as part of the WWE Supplemental Draft while Nitro was drafted to ECW.
Dykstra made his debut on the July 6, 2007 episode of SmackDown! in a losing effort to the re-debuting Chuck Palumbo. On the July 20, 2007 episode of SmackDown!, Dykstra participated in a 20 man battle royal for the World Heavyweight Championship and was eliminated by Chris Masters; later on that evening, he lost to Matt Hardy in singles competition.
Dykstra formed an on-screen relationship with Victoria on the July 27 episode of SmackDown!. The two teamed together in mixed tag team matches, usually against Jimmy Wang Yang and Torrie Wilson or Chuck Palumbo and Michelle McCool. They also regularly accompanied each other to the ring for matches.
After a leave of absence from television in the first half of 2008, Dykstra made his return on the August 15 episode of SmackDown, losing to WWE Champion Triple H. On November 10, 2008, WWE announced Dykstra had been released from his contract.
On November 15, 2011, Dykstra wrestled a dark match for WWE at the SmackDown tapings in Bridgeport, Connecticut, losing to Justin Gabriel.
Dykstra made a one night return to WWE on the October 4 edition of Smackdown Live along with Mikey in their Spirit Squad characters, appearing in a segment where they would taunt Dolph Ziggler about his time in the Spirit Squad. They would then attack Ziggler on orders from The Miz until Ziggler fought back and took them both out. Five days later, at the No Mercy pay-per-view, he and Mikey tried to distract Ziggler in his Career vs. title match under Maryse's command, but were unsuccessful in doing so, ultimately giving Ziggler the win. On the October 11 episode of WWE Smackdown, Kenny along with Mikey made their return to the ring as the duo took on Dolph Ziggler in a 2-on-1 Handicap match, which Dolph won. On the October 18 episode of WWE SmackDown, Kenny, Mikey, and the Miz defeated Dolph Ziggler, Heath Slater and Rhyno in a six-man tag team match with Kenny pinning Slater.