London signed with World Wrestling Entertainment (WWE) in mid–2003, working a few dark matches. London made his official WWE television debut on the SmackDown! brand, losing to Brock Lesnar in a match for the WWE Championship on October 9. After the match, Lesnar continued to attack London until fellow cruiserweight Spanky (Brian Kendrick) made the save. The two competed as a tag team on SmackDown!'s sister show Velocity until Spanky left the company in January 2004.
London then began a tag team with Billy Kidman on January 29, 2004. On the July 8 episode of SmackDown!, the duo won the WWE Tag Team Championship from the Dudley Boyz. They defended the title against the Dudleys and the Basham Brothers on several occasions before losing the championship to René Duprée and Kenzo Suzuki on September 9, due to Kidman leaving London to fight by himself. Kidman's heel turn led to a feud between the two, which culminated at No Mercy where Kidman defeated London with a shooting star press. After the match, London was bleeding from the mouth and being stretchered when Kidman pulled him back into the ring with the stretcher and delivered another shooting star press to London's injured ribs. This storyline was put in place after London had broken his nose wrestling Booker T and needed time off to recuperate. London returned on November 25, wrestling on Velocity until the end of the year.
On March 10, 2005, London became the number one contender for Chavo Guerrero's WWE Cruiserweight Championship, which he later won in a cruiserweight battle royal. Guerrero challenged London for the title at Judgment Day, where London emerged victorious. During another title match with Guerrero on June 23, The Mexicools stormed the ring, attacking both London and Guerrero. On the July 14 episode of SmackDown!, London teamed with Scotty 2 Hotty and Funaki to face The Mexicools. The ending of the match saw Juventud perform the 450° splash on London for the win, but landed his knee onto London's face and legitimately broke his nose in the process. London lost the Cruiserweight Title on the August 4 episode of Velocity to Nunzio. Later in the night, London cut a heel promo encouraging the fans to protest his title loss. London went on a losing streak before returning as a face and teaming with the newly rehired Brian Kendrick.
On the December 16 episode of Velocity London and Kendrick remade their image, wearing theatrical masks to the ring and matching vests and shorts. On the April 7, 2006 episode of SmackDown!, London and Kendrick defeated WWE Tag Team Champions MNM in a non-title match. They developed a winning streak over the champions, including singles victories for both Kendrick and London over Johnny Nitro and Joey Mercury, respectively. London and Kendrick won the WWE Tag Team Championship at Judgment Day, marking consecutive victories for London and Kendrick over MNM. On August 11, K. C. James and Idol Stevens defeated the champions in a non-title match, igniting a feud between the two teams. During the rivalry, WWE Diva Ashley Massaro began accompanying London and Kendrick to the ring to act as a valet and combat the actions of James and Stevens' manager Michelle McCool.
They soon began a losing streak to the team of William Regal and Dave Taylor. Regal defeated both team members in singles matches and on the December 8 episode of SmackDown!, Kendrick and London lost a tag team match to the pair. As a result, they were scheduled to defend the championship against Regal and Taylor at Armageddon; at the event, the match was changed to a four-way ladder match also involving MNM and The Hardys. London and Kendrick won the match and retained the championship. On the January 12, 2007, episode of SmackDown! London and Kendrick successfully retained their championship against Regal and Taylor in a traditional tag team match.
On February 2, London and Kendrick suffered a non-title loss to the rookie team Deuce 'n Domino. A further tag team match loss and a singles loss for Kendrick to Deuce led to a championship match at No Way Out, in which London and Kendrick were victorious. They retained the championship against MNM on SmackDown in March, and then retained the championship against Deuce 'n Domino again in April, after Deuce 'n Domino were disqualified. In a rematch the following week on the April 20 episode of SmackDown!, London and Kendrick lost the championship to Deuce 'n Domino. During the match London missed a moonsault from the ring apron to the floor kayfabe injuring his ribs, leaving Kendrick to battle Deuce 'n Domino alone. London and Kendrick's reign is the longest in the championship's history at 331 days. Selling his storyline injured ribs, London was absent from physical action until the May 11 episode of SmackDown, when he defeated Domino in singles competition. London and Kendrick unsuccessfully competed for the title on June 1 in a triple threat tag team match, which also involved Regal and Taylor, and lost a rematch on June 15 in a standard tag team match.
Both London and Kendrick were drafted to the Raw brand on June 17, 2007, during the Supplemental Draft. They won their debut match on Raw against The World's Greatest Tag Team on June 18. Throughout July and August, they wrestled against The World's Greatest Tag Team and Lance Cade and Trevor Murdoch on Raw, and on September 3, they won a number one contender's match for Cade and Murdoch's World Tag Team Championship. At a house show in South Africa on September 5, London and Kendrick defeated Cade and Murdoch to win the World Tag Team Championship, only to lose it back in a rematch three days later. At the end of 2007, he was inactive due to a foot injury. London returned on the February 4, 2008, episode of Raw, when he and Kendrick lost to the team of Carlito and Santino Marella. On the March 17 episode of Raw, London and Kendrick faced Umaga in a handicap match. During the match, Kendrick walked out and left London to get pinned; no dissension came of the incident, and London and Kendrick continued to team together. They unsuccessfully challenged Hardcore Holly and Cody Rhodes for the World Tag Team Championship on May 26.
The team came to an end when Kendrick was drafted back to the SmackDown brand as part of the 2008 WWE Supplemental Draft in June. The following month, London was briefly involved in a storyline between Shawn Michaels, and Chris Jericho and Lance Cade, when Jericho and Cade used London as an example of what happened to those who idolized Michaels. London lost singles matches to both Jericho and Cade on Raw, before disappearing from television. London was released from his WWE contract on November 7, 2008.