Despite an earlier bitter feud, Walsh had a public reconciliation with Boyzone on the ITV2 programme Ghosthunting With... in which they explored a network of subterranean streets beneath Edinburgh.

The following year Walsh appeared as a judge on the UK ITV show Popstars: The Rivals with Pete Waterman and Geri Halliwell.

[citation needed] Walsh managed the band to achieve a million singles sales while their debut album went platinum.

[citation needed] Walsh also frequently appears on various talent shows on Raidió Teilifís Éireann (RTÉ), the most recent[when?]

In January 2012, Walsh appeared on the ITV documentary series The Talent Show Story where he was interviewed about being a judge on The X Factor and Popstars The Rivals.

[citation needed] In 2005, Walsh managed the winner Shayne Ward, whose debut single "That's My Goal" spent four weeks at UK number one.

[6] Walsh returned on the Saturday evening's live show, stating that he could not abandon his remaining competitor and eventual winner, Shayne Ward.

[citation needed] ITV announced in March 2007 that Walsh would not return as a judge on The X Factor, but would remain behind the scenes managing some acts from the show.

In the 'Judges Houses' stage of the competition, Walsh took his acts to Dublin and invited guest Kian Egan to help him decide whom to take through to the live shows.

Walsh took his acts to Castle Leslie in Ireland during the judges houses stage where he was aided by Westlife star Shane Filan.

Kandy Rain were eliminated in the first live results show, from which Walsh was absent due to the sudden death of Boyzone member Stephen Gately.

[citation needed] Walsh was absent again on the Saturday and Sunday of the second week of live shows due to Gately's funeral on 17 October.

He joined new panellists Gary Barlow, Kelly Rowland and Tulisa, who replaced former judges Cowell, Minogue and Cole, all of whom left the show after series seven.

He joined the other season two judges: L.A. Reid, Demi Lovato and Britney Spears, and was introduced with the line, "When Simon needs an opinion from someone he trusts, I'm the man he calls".

[11] Walsh returned for the tenth series and was joined by Barlow, Scherzinger and fellow original judge Osbourne, who replaced Tulisa.

Despite not winning, this was still by far Walsh's most successful year as a judge on the show due to going 5 weeks (breaking a record) without having any of his acts in the bottom two and had two of them (Friend and McDonald) in the final.

On 7 June 2018, Walsh announced he had decided not to return for the fifteenth series, in order to focus on music management and other commitments.

In July 2011, he raced the "Reasonably Priced Car", a Kia Cee'd, during series 17 of Top Gear[19] On 1 September 2014, Walsh appeared on an episode of Who's Doing the Dishes?

Hosted by Vernon Kay, the show began airing on 5 April 2016[21] In 2023 he was a guest on Channel 5's Eurovision: 30 Unforgettable Moments a chart countdown based on the song contest which also featured contributions from David and Carrie Grant, The Fizz and Johnny Logan, with footage from the 1980s' contest showing Walsh cheering on Logan included in the run time.

[24] During his stint in Celebrity Big Brother, Walsh revealed that he had survived a diagnosis of Waldenström macroglobulinemia, a rare form of blood cancer, in 2020 during the height of the COVID-19 pandemic.

[35] Walsh sought access to documents which allegedly showed that The Sun UK tabloid paid €700 to a man who made a false sexual assault accusation against him.

[40] Despite winning the legal case, the false accusations had a "lasting effect" on Walsh who was, as of 2015, suffering from paranoid thoughts and panic attacks as a result of the ordeal.

[42][43] During an interview conducted by Sarah-Jane Crawford on The Xtra Factor during the semi-final results show in 2014, Walsh groped Mel B by her buttocks.

[45][46] Walsh stated on 21 July 2018 that he grabbed Mel B's buttocks as a joke, but conceded that the gesture was no longer "politically correct" due to social media reaction.

[47] Misha B, a contestant from the 2011 series of The X Factor, stated in June 2020 that she had been a victim of racism and accusations made by Walsh and Tulisa, who were judges on the show at the time.