[10] In 1998, Molloy sang the song "Black and White Army (Bringing The Pride Back Home)" written by Sting for the Newcastle's 1998 FA Cup final.

[7] On 31 October 2004, Molloy was chosen from 200 candidates as the new lead singer of Frankie Goes to Hollywood, appearing on 11 November in a special charity show for The Prince’s Trust at Wembley Arena celebrating Trevor Horn's 25 years as a record producer,[5][11] performing live "Welcome to the Pleasuredome", "Two Tribes", and "Relax".

[5][15][16] He spent some time in 2005 also working with Dave Stewart of Eurythmics on the spoof documentary Platinum Weird, which involved Christina Aguilera, Gwen Stefani and Carmen Electra.

[30] In April 2017, held a concert "Big in Japan" (pun on his size[18]) in Tokyo, collaborating with producer Andy Wright and guitarist Kenji Suzuki from Simply Red.

[35][18] In 2004, he gained a chorus role in the controversial production of Jerry Springer – The Opera, where Molloy was a member of the original cast at the National Theatre, and went on to play the parts of the transvestite Tremont and the Angel Gabriel.

[5] In early 2006 had to do appendix operation,[5] but managed get the role of Stuart in the touring production of Ben Elton's Rod Stewart musical, Tonight's The Night.

[38] In September-October played as John the Baptist and Judas in Godspell,[39] with theatre critics Mark Shenton and Sam Marlower praising his projection of charisma,[40] being one of "few bright spots".

In October 2007, Molloy was cast as Frankie Valli in the West End premiere of Jersey Boys at the Prince Edward Theatre, and played his first preview performance on 28 February 2008, and official opening on 18 March 2008.

[27][49] Molloy also provided vocals in the 2014 soundtrack (particularly "Beggin'") of the film version of the musical directed by Clint Eastwood, for which also auditioned but was chosen John Lloyd Young instead.

[56] In September-October 2016 at Cockpit Theatre, Marylebone, played Hades/Devil in a rock musical 27 choreographed and co-directed by Arlene Phillips,[57][58] partly based on Greek mythology, telling "the story of a musician following a path of self-destruction at the age of 27".

[2] He "was obsessed with John Hughes movies as a kid",[68] Barbra Streisand's Hello Dolly soundtrack was his childhood introduction to performance, while Donny Hathaway's Collection inspired his voice and style.