Leona Lewis, the winner of the third series of The X Factor, was signed to Cowell's label Syco and has had number one singles and album sales around the world. Cowell returned for a fourth series on 18 August 2007 alongside Osbourne, Walsh and new judge, Dannii Minogue. Walsh had previously been sacked from the judging panel by Cowell for the fourth series, and he was subsequently replaced by Brian Friedman, who was a judge on Grease Is the Word. Walsh was later brought back by Cowell a week into the auditions when he and Osbourne realised that they missed Walsh and that without him, there was no chemistry between the judges. Cowell returned for the fifth series in 2008, with Walsh, Minogue, and new judge Cheryl Cole, as Osbourne had decided to quit before the show began. Cowell returned for series 6 and 7 as well, although series 7 was to be his last, as he left in 2011 in order to launch The X Factor in America. After placing third in the seventh series of The X Factor in the UK, boyband One Direction signed to Cowell's label in 2011, and the group has gone on to top singles and album charts worldwide. Cowell was replaced by Gary Barlow. In 2011, UK series eight winners Little Mix signed to Cowell's label. The girl group has sold 50 million records worldwide.
Britain's Got Talent debuted on ITV in June 2007. Cowell appeared as a judge alongside Amanda Holden and Piers Morgan. The show was a ratings success, and second and third seasons followed in 2008 and 2009. The third series featured a publicity coup when Susan Boyle made a global media impact comparable to that of any previous talent show series winner with her regional audition performance. In December 2019, Cowell signed a five-year deal with ITV ensuring Britain's Got Talent will stay on the channel until 2024.
Cowell was also the executive producer of Grease Is the Word for ITV. This show set out to find performers to play Danny and Sandy in the 2007 West End revival of Grease. It was hosted by Zoë Ball and judged by Britons David Ian and Sinitta and Americans David Gest and Brian Friedman. The musical theatre casting concept had already been introduced by the BBC with the ratings hit How Do You Solve a Problem like Maria?, but Cowell's show was not the hoped-for success. He himself said, "It has been slaughtered by the critics – and rightly so. It is far too similar to our other formats."
Cowell was once the fastest "Star in a Reasonably Priced Car" on BBC's motoring show Top Gear, driving a Suzuki Liana around the show's test track in a time of 1:47.1. When Top Gear retired the Liana along with its rankings after the eighth series, Cowell was the eighth fastest overall and the third fastest non-professional driver. On 11 November 2007 Cowell yet again appeared on Top Gear, achieving a time of 1:45.9 thus putting him ahead of chef Gordon Ramsay and back at the top of the table. His time of 1:45.9 was then tied with English rock singer Brian Johnson of AC/DC and Grand Designs host Kevin McCloud for the second fastest time, just 0.1 seconds behind Jamiroquai singer Jay Kay. In March 2015, Cowell backed Top Gear presenter Jeremy Clarkson after he was suspended by the BBC for punching a colleague, with Cowell stating on Good Morning Britain: "He's apologised. But I think what is quite obvious is that the public are behind him, but you know, that's Jeremy."
Cowell was a partner in the Royal Ascot Racing Club, a thoroughbred horse racing syndicate which owned the 2005 Epsom Derby winner, Motivator. Cowell was chosen as the first subject of the re-launched This Is Your Life, in an episode broadcast on 2 June 2007. He was presented with the Red Book by Sir Trevor McDonald while presenting American Idol.
On 1 July 2007, Cowell appeared as a speaker at the Concert for Diana (alongside Randy Jackson and Ryan Seacrest) held at Wembley Stadium, London, to celebrate the life of Princess Diana almost 10 years after her death. Proceeds from the concert went to Diana's charities as well as to charities of which her sons Princes William and Harry are patrons.