On May 26, 2006, Hornswoggle made his WWE debut in Bakersfield, California on SmackDown, as the character Little Bastard, the leprechaun partner of Finlay. After Finlay's victory over Paul Burchill, an extremely hyper, dirty, mysterious little man in a leprechaun costume scurried out from under the ring and jumped on Burchill, laughing maniacally. Finlay pulled him off, only to slam him back down onto Burchill again and again. For the next few weeks, he continued to appear from under the ring after matches and attack Finlay's opponents. He soon became more and more aggressive and started attacking Finlay's opponents during matches, much to Finlay's dismay. At one point, he attacked Finlay, biting him when Finlay tried to stop him from attacking Gunner Scott. Little Bastard helped Finlay win the WWE United States Championship when he tossed him a shillelagh to knock out the champion Bobby Lashley and pick up the win.
On February 23, 2007, the character's name was changed to Hornswoggle on WWE's website and all references to the name "Little Bastard" were removed. On the March 2 episode of SmackDown!, Hornswoggle attacked John "Bradshaw" Layfield and Michael Cole. Afterward, Finlay intimidated Cole, warning him to refer to Little Bastard as "Hornswoggle." On March 30, Hornswoggle helped Finlay beat Mr. Kennedy by performing a senton bomb off a stepladder onto Mr. Kennedy, essentially copying Kennedy's move, the Kenton Bomb. SmackDown! announcers Michael Cole and JBL immediately referred to the move as the "Lepreton Bomb". During the Money in the Bank ladder match at WrestleMania 23, Kennedy hit Hornswoggle with a Green Bay Plunge off of a ladder when Hornswoggle tried to interfere on the behalf on Finlay. On the following edition of SmackDown!, Finlay attacked Mr. Kennedy after his match and challenged him to a handicap match with Hornswoggle as Finlay's partner. Before the match, Mr. Kennedy apologized for hurting Hornswoggle. Finlay accepted his apology and formed a team with Kennedy.
Hornswoggle won the WWE Cruiserweight Championship after he pinned Jamie Noble in a Cruiserweight Open at The Great American Bash. The other participants and commentators were unaware that he was a participant in the match until the referee counted the pin and awarded him the belt. Hornswoggle then began a storyline feud with Noble over the belt. The next week on SmackDown!, Hornswoggle retained the title when he defeated Noble by countout. He attacked Noble in the following weeks by shoving a pie in his face, spraying him with a fire extinguisher, pushing him into Kane and causing him to get chokeslammed, and locking him in a large box.
On the September 10 episode of Raw, the storyline involving Mr. McMahon's illegitimate son culminated with the reveal that Hornswoggle was the illegitimate son. Hornswoggle's feud with Noble ended on September 28 on SmackDown! when acting General Manager Vickie Guerrero forced Hornswoggle to surrender the Cruiserweight Championship (which was later abandoned), citing that his status as Mr. McMahon's son and his diminutive stature would eventually jeopardize his well-being. Mr. McMahon began giving Hornswoggle matches against competitors that were much larger than him to show his son "tough love." Hornswoggle was placed into a match against The Great Khali at Survivor Series. At the event, Khali defeated Hornswoggle by disqualification when Finlay attacked Khali on Hornswoggle's behalf, turning both Hornswoggle and Finlay faces. This was the first time that Finlay appeared together with Hornswoggle since the beginning of the Hornswoggle and Mr. McMahon storyline. At Armageddon, Finlay defeated Khali with the help of Hornswoggle. In addition, Hornswoggle also faced Khali on the 15th Anniversary of Raw, but Hulk Hogan made a surprise return in a one night appearance to come to Hornswoggle's aid.
On the February 18 episode of Raw, Hornswoggle had a scheduled steel cage match against his father, Mr. McMahon. During this match, Hornswoggle was whipped with a leather belt by Mr. McMahon. Finlay tried to get involved, but was attacked and handcuffed to the ring ropes by JBL. Mr. McMahon left the ring and allowed JBL to beat up Hornswoggle while an enraged Finlay watched. Following the attack, as a part of the storyline, WWE.com announced that Hornswoggle had suffered internal injuries, including bleeding of the brain and spinal trauma. On February 25, JBL claimed that Hornswoggle is not Mr. McMahon's son, but "in reality is the son of Finlay". The next week on Raw, Finlay confirmed Hornswoggle was indeed his son, then was forced to watch helplessly as JBL assaulted Hornswoggle in his hospital bed. Hornswoggle returned to live television at WrestleMania XXIV, accompanying Finlay to the ring for his Belfast Brawl with JBL, once interfering by hitting JBL with a kendo stick, allowing Finlay to get the shot in with the shillelagh. JBL won the match by hitting Finlay with the kendo stick in the shins and following up with the Clothesline from Hell.
He made his in-ring return on the April 18 episode of SmackDown, defeating Matt Striker after a Tadpole Splash. As part of the 2008 WWE Supplemental Draft, Hornswoggle was drafted to the ECW brand along with Finlay. At Night of Champions, Hornswoggle and Finlay challenged John Morrison and The Miz for the WWE Tag Team Championship, but failed to win.
On April 13, 2009, Hornswoggle was drafted to the Raw brand, without Finlay, as part of the 2009 Supplemental Draft. Hornswoggle then entered into a feud with Chavo Guerrero, in which they competed in a series of comedy gimmick matches each week determined by the weekly guest host for Raw (Texas Bullrope Match, Blindfold Match, Falls Count Anywhere, etc.). The program began on July 7, 2009 on WWE Superstars and continued on to Raw. Hornswoggle won every match in this feud.
His next storyline began the October 26 episode of Raw, when after several weeks of wearing D-Generation X clothing, Hornswoggle received legal notification that he was no longer allowed to wear it. Later on in the night, he got his revenge by helping the Raw guest hosts, Kyle Busch and Joey Logano, put DX against each other and John Cena for the WWE Championship at Survivor Series. On the December 21 episode of Raw, Hornswoggle tried pressing charges against DX for assault on him, but later dropped them when DX agreed to make him DX's official mascot. On the January 18, 2010 episode of Raw backstage, Hornswoggle and Triple H confronted Big Show, The Miz and Jon Heder. Triple H made the match a six-man tag team match: DX and Hornswoggle against The Big Show, The Miz and Jon Heder which ended after Hornswoggle pinned Heder.
As part of the 2010 WWE Supplemental Draft on WWE.com, Hornswoggle was drafted back to the SmackDown brand. On the October 8 episode of SmackDown, Hornswoggle was named the official mascot for the SmackDown team at Bragging Rights. On the July 9, 2012 episode of Raw, Hornswoggle was revealed as the Anonymous Raw General Manager, who previously ran the brand from June 2010 to July 2011.
On the season premiere of NXT Redemption, Hornswoggle was revealed as the pro for Titus O'Neil. After their tag team victory over Darren Young and Chavo Guerrero, Young attacked O'Neil. They later had a match against each other which Hornswoggle won. Hornswoggle was later confronted by O'Neil's previous NXT mentor, Zack Ryder. Ryder lured Titus out of the ring by pretending to attack Hornswoggle, but he quickly re-entered the ring and ambushed Titus as he climbed back in, cementing the victory. Weeks later, Hornswoggle was sent gifts from a secret admirer, assuming it to be Maryse. He responded by giving her gifts, only to be shot down. On July 26, AJ Lee revealed herself as the admirer by kissing him. AJ then accompanied Hornswoggle on both NXT and SmackDown. Some time later, Hornswoggle became jealous of O'Neil hugging AJ and eventually sent her a letter ending their relationship, as he no longer wanted to be on NXT and preferred to stay on SmackDown.
On the November 29, 2011, holiday edition of SmackDown, Hornswoggle won a battle royal, by lastly eliminating Sheamus, to receive a wish from Santa Claus (Mick Foley). With help from Sheamus, Hornswoggle wished for the ability to verbally communicate. With this ability, Hornswoggle became the special guest ring announcer for the David Otunga and Sheamus match on the following week's SmackDown. On the January 6, 2012, episode of SmackDown, he defeated Heath Slater in an Over the Top Rope Challenge. Later that month, Hornswoggle formed an alliance with Justin Gabriel, feuding with the former Intercontinental Champion Cody Rhodes and Heath Slater, he also accompanied Gabriel to the ring at the Elimination Chamber pay-per-view in a losing effort against United States Champion Jack Swagger. On the March 23 episode of SmackDown, Hornswoggle was added to Theodore Long's WrestleMania XXVIII team as its personal mascot.
He made a return on October 12, 2012, when he was found with a Randy Orton doll. Ricardo Rodriguez wrecked it and continued looking for the real Orton. After a period of inactivity, he returned to Raw in November, associating himself with The Great Khali and Natalya. He was injured by Big E Langston on the January 11, 2013 episode of SmackDown, after Khali and Natalya lost to Dolph Ziggler and AJ Lee. He returned on the March 17 episode of Raw, to celebrate St. Patrick's Day, only to be interrupted by Bad News Barrett.
On the April 15, 2014 episode of Main Event, Hornswoggle turned heel for the first time since 2007 after revealing himself as the mascot for 3MB (Heath Slater, Drew McIntyre and Jinder Mahal). In the following months, he faced El Torito numerous times, losing a WeeLC match at Extreme Rules and a hair match at Payback, resulting in his head being shaved. On June 12, 2014, McIntyre and Mahal were released by WWE, ending 3MB. In July on Superstars, Hornswoggle accompanied Slater for his match with Adam Rose, and was kidnapped by the Rosebuds, who transformed him into a mini-Rose. On the August 19 episode of Main Event, Hornswoggle joined his former rivals, Los Matadores (including El Torito), as their second valet. Hornswoggle donned a cow suit and was referred to as La Vaquita, to complement El Torito, who was dressed as a tiny bull. Los Matadores went on to be defeated by Heath Slater and Titus O'Neil. That same week, on Superstars, his name was tweaked to La Vaca, when he teamed with El Torito to defeat Slater and O'Neil. On the September 29 episode of Raw, Hornswoggle turned heel once again and became Slater and O'Neil's mascot, the Mini-Gator. After the breakup of Slater-Gator, he took time off from WWE television to undergo surgery in March 2015.
On September 28, 2015, WWE announced it had suspended Hornswoggle for 30 days for violating the company's Wellness Policy. After not having made any appearances in WWE since then, Hornswoggle was released from WWE on May 6, 2016.
On April 27, 2018, Hornswoggle returned as a face for the first time since 2014 in the Greatest Royal Rumble event, eliminating Dash Wilder, before being eliminated himself by Tony Nese. On January 27, 2019, he made an appearance at the Royal Rumble during the women's Rumble match. He remained under the ring throughout the majority of the match until he chased around Zelina Vega, who spent the majority of her time in the match hiding under the ring.