Ciampa appeared on the July 14, 2005, episode of SmackDown as Thomas Whitney, ESQ, one of Muhammad Hassan's lawyers and confronted The Undertaker. Tommaso read a statement from Hassan before being attacked by The Undertaker. On the December 17 episode of Velocity, under the ring name Demarso Whitney, he was defeated by Jamie Noble. On the August 25, 2006 episode of Heat, he and Kofi Kingston had a dark match against Lance Cade and Trevor Murdoch.
Although not re-signed to WWE, on September 2, 2015, Ciampa was announced as part of the NXT Dusty Rhodes Tag Team Classic tournament. On September 9, he successfully advanced in the first round of the tournament alongside his new partner Johnny Gargano, defeating the also newly-formed duo of Tyler Breeze and Bull Dempsey. On the September 16 episode of NXT, Ciampa and Gargano lost to Baron Corbin and Rhyno, thus eliminating them from the tournament. On the September 30 episode, Ciampa lost to Breeze in a singles match. He appeared on the December 2 episode of NXT, losing to Samoa Joe. Ciampa won a match against Danny Burch on the January 13, 2016, episode of NXT and defeated Bull Dempsey on the February 24, episode. On March 15 tapings, Ciampa scored another win, this time against Jesse Sorensen.
On April 2, 2016, it was confirmed that Ciampa had signed with WWE earlier in the week. On June 23, Ciampa entered the Cruiserweight Classic tournament, losing to Johnny Gargano in his first round match. On August 20 at NXT TakeOver: Brooklyn II, Ciampa and Gargano unsuccessfully challenged The Revival (Dash Wilder and Scott Dawson) for the NXT Tag Team Championship. Ciampa and Gargano, now collectively billed as "#DIY", received another title shot in a two out of three falls match on November 19 at NXT TakeOver: Toronto, where they defeated The Revival to become the new NXT Tag Team Champions.
DIY went on to successfully defend their championships against the team of Tajiri and Akira Tozawa and TM61 in Japan and Australia, respectively. They retained their titles against The Revival on the January 11, 2017 episode of NXT, but were attacked by The Authors of Pain (Akam and Rezar) afterwards. Ciampa and Gargano lost the championships to The Authors of Pain at NXT TakeOver: San Antonio. They would get their rematch on the March 1 episode of NXT, which ended in a no contest after The Revival interfered and attacked both teams. This led to NXT TakeOver: Orlando, a triple threat elimination match between all three teams for the titles, but DIY were unsuccessful after being the first team eliminated.
At NXT TakeOver: Chicago, DIY faced The Authors of Pain in the first-ever ladder match for the NXT Tag Team Championship, which they lost. After the match, Ciampa attacked Gargano, turning heel and disbanding #DIY. It was later revealed that Ciampa had suffered a ruptured ACL in his right knee during the ladder match and would await surgery. In a further update, it was reported that his surgery was successful and the timetable for his return was estimated for early-to-mid 2018.
On January 27, 2018, Ciampa returned at NXT TakeOver: Philadelphia, attacking Gargano with a crutch to close the show. He then cost Gargano his NXT Championship match against Andrade "Cien" Almas on the February 21 episode of NXT, forcing Gargano to leave NXT as per the pre-match stipulation. Ciampa made his in-ring return in the main event of NXT TakeOver: New Orleans, losing to Gargano in an unsanctioned match, resulting in Gargano being reinstated to NXT. Their feud would continue throughout the following weeks in which they attacked each other and interfered in each other's matches, leading to a Chicago Street Fight at NXT TakeOver: Chicago II, which Ciampa won.
On the July 18 tapings of the July 25 episode of NXT, Ciampa defeated Aleister Black to capture the NXT Championship after Gargano interfered and accidentally hit Black with the title belt. This made Ciampa only the second wrestler to hold both the NXT Championship and NXT Tag Team Championship, after Neville. At NXT TakeOver: Brooklyn IV, he was scheduled to defend the title against Black and Gargano in a triple threat match, but Black was removed from the match due to being ambushed in the arena parking lot by an unknown assailant (in reality, Black had suffered a legitimate groin injury). The match was changed to the first-ever Last Man Standing match for the NXT Championship between Ciampa and Gargano, where Ciampa retained his title. At NXT TakeOver: WarGames, Ciampa retained the championship against Velveteen Dream. Ciampa faced Black for the championship at NXT TakeOver: Phoenix, in a winning effort.
Ciampa debuted on Raw on February 18, 2019 with three other fellow NXT stars Johnny Gargano, Aleister Black and Ricochet. In his debut match on Raw, he and Gargano defeated Raw Tag Team Champions The Revival. The next night on SmackDown Live, Ciampa and Gargano defeated The Bar (Cesaro and Sheamus). On March 6, it was reported that Ciampa would have to undergo neck surgery, thus forcing him to vacate the NXT Championship. At that point, he had not wrestled since February 19. WWE later confirmed the story saying he would undergo an anterior cervical fusion.
On March 13, 2019 tapings of NXT (airing March 20), Ciampa relinquished his NXT Championship, thus ending his reign at 237 days. Ciampa gave an update on April 1, saying that if he is able to return to the ring, doctors say he will be on "borrowed time". Ciampa made a surprise appearance at NXT TakeOver: New York after Gargano defeated Adam Cole to win the NXT Championship, and embraced Gargano to celebrate his victory.
On the October 2 episode of NXT, Ciampa returned from injury as a face by confronting Adam Cole and his NXT Championship. After Ciampa saved Matt Riddle and Keith Lee from a beatdown at the hands of The Undisputed Era (Cole, Bobby Fish, Kyle O'Reilly, and Roderick Strong) on the October 30 episode of NXT, a WarGames match was scheduled between Ciampa's team against The Undisputed Era. At NXT TakeOver: WarGames on November 23, Team Ciampa (Ciampa, Lee, Dominik Dijakovic, and Kevin Owens) defeated The Undisputed Era. This led to a match between Ciampa and Cole at NXT TakeOver: Portland on February 16, 2020 for the NXT Championship, which Cole won after Johnny Gargano cost Ciampa the match, thus re-igniting their feud. On the April 8 episode of NXT, this culminated in a No Holds Barred match between Ciampa and Gargano, which Gargano won after interference from Candice LeRae.
Ciampa would then enter a feud with Karrion Kross, who attacked him backstage during an interview. At NXT TakeOver: In Your House, Ciampa was quickly defeated by Kross. After a brief hiatus, Ciampa returned on the August 26 episode of NXT, where he defeated Jake Atlas and would continue his post-match assault on Atlas, thus turning heel in the process. He would then compete in a losing effort in the fatal four-way sixty minute Iron Man match for the vacant NXT Championship, tying with Gargano at one fall a piece. Ciampa turned face again when he began a feud with Timothy Thatcher, which led to a match at NXT TakeOver: WarGames, where Ciampa won. On the January 20, 2021 episode of NXT, Ciampa fought Thatcher in the Fight Pit, where he lost. After the match, Thatcher and Ciampa showed respect to one another and Ciampa asked Thatcher to be his partner for the Dusty Rhodes Tag Team Classic, which Thatcher accepted. They defeated Ariya Daivari and Tony Nese in the first round and The Undisputed Era (Adam Cole and Roderick Strong) in the quarterfinals, before being defeated by the Grizzled Young Veterans in the semi-finals. At NXT TakeOver: Stand and Deliver, Ciampa was defeated by Walter in a match for the NXT UK Championship. On the June 15 episode of NXT, Ciampa and Thatcher defeated the Grizzled Young Veterans in a tornado tag match to earn a future NXT Tag Team Championship match. They faced the champions MSK on July 6 at The Great American Bash, but were defeated.
On the September 14 edition of NXT, Ciampa defeated LA Knight, Pete Dunne, and Von Wagner in a fatal four-way match to win the vacant NXT Championship. At Halloween Havoc, Ciampa successfully retained his title against Bron Breakker. At WarGames, Ciampa teamed with Johnny Gargano, LA Knight and Pete Dunne (as "Team Black & Gold") against Breakker, Carmelo Hayes, Grayson Waller, and Tony D'Angelo (as "Team 2.0"), but were defeated after Breakker pinned Ciampa. At New Year's Evil on January 4, 2022, Ciampa lost the title to Breakker in a rematch, ending his second reign at 112 days. On April 2 at NXT Stand and Deliver, Ciampa would be defeated by Tony D'Angelo in what would be his final match in NXT.
On the April 11 episode of Raw, Ciampa would be revealed as a new member of the Raw roster in a backstage segment with Ezekiel and Kevin Owens. On the April 25 episode of Raw, Ciampa would turn heel after he attacked a returning Mustafa Ali following his match with The Miz. During this time, his name would be shortened to Ciampa. On the July 4 episode of Raw, Ciampa aligned himself with The Miz after helping him attack AJ Styles after their match. On the August 1 episode of Raw, Ciampa defeated Dolph Ziggler and Chad Gable in a triple threat match while also defeating Styles later that night to earn an opportunity to face Bobby Lashley for the United States Championship. Ciampa faced Lashley for the title the following week in a match dedicated to Harley Race, but lost. On the September 5 episode of Raw, his ring name was reverted back to Tommaso Ciampa.
On the June 19, 2023 episode of Raw, Ciampa returned after a prolonged injury to answer The Miz's open challenge. Ciampa won, ending their alliance and turning Ciampa face once again. In late September, Ciampa began a feud with Intercontinental Champion Gunther, losing a match for the title on on the October 2 episode of Raw. Post-match, after a five month hiatus, Johnny Gargano returned and saved Ciampa from an attack from Imperium, reforming DIY. On the January 8, 2024 episode of Raw, Ciampa beat Finn Balor, earning DIY a tag team title shot. They got the match on the January 29 episode of Raw, but were defeated by The Judgment Day. On the March 18 episode of Raw, DIY defeated the Creed Brothers to qualify for the six-pack tag team ladder match for the Undisputed WWE Tag Team Championships at WrestleMania XL, which they were unsuccessful. On the April 15 episode of Raw, DIY defeated The New Day and the Creed Brothers to face Awesome Truth (The Miz and R-Truth) for the renamed World Tag Team Championships, where Awesome Truth retained.
On night two of the 2024 WWE Draft, both Ciampa and Gargano were drafted to SmackDown. On the May 31 episode of SmackDown, Ciampa defeated one half of the WWE Tag Team Champions Austin Theory. On the July 5 episode of SmackDown, Ciampa and Gargano defeated A-Town Down Under (Theory and Grayson Waller) to become the new WWE Tag Team Champions. On the August 2 episode of SmackDown, DIY lost the titles to The Bloodline (Jacob Fatu and Tama Tonga) after interference from Solo Sikoa and Tonga Loa, ending their reign at 28 days. Over the next few months, DIY vowed to win back the titles, but there were signs of dissension between Ciampa and Gargano as the former took on a more aggressive character. On the November 15 episode of SmackDown, Ciampa interrupted a title match between The Street Profits (Angelo Dawkins and Montez Ford) and defending champions Motor City Machine Guns (Alex Shelley and Chris Sabin), attacking both teams, but Gargano restrained him. On the December 6 episode of SmackDown, DIY defeated Motor City Machine Guns to win the titles for the second time after Gargano hit Sabin with a low blow, and later revealing the recent arguments to all be a ruse, turning Gargano heel for the first time since 2021 and the first time on the main roster and as a team.