Finn was born in Thornton Heath, Surrey. After he joined Tyrannosaurus Rex in late 1969, it was rumoured that Bolan had hired Finn for his good looks, and because he admired his motorcycle, rather than for his musical ability. Finn was unable to recreate the complex rhythmical patterns of his predecessor, Steve Peregrin Took, and was effectively hired as much for a visual foil for Bolan as for his drumming. The BBC news commented on this, saying "Marc Bolan was supposed to have said of Finn: 'He can't sing... but he looks superb.'"[1]
Mickey Finn stated, on a radio show in Denmark on which he and Marc Bolan were appearing as guest DJs, that his big influence in percussion was the prolific Master Henry Gibson from Curtis Mayfield's band.[citation needed] In 1969–1971, Finn's contribution to Bolan's music, as bongocero, backing vocalist and occasional bass guitarist, was essential, because T. Rex started off as Tyrannosaurus Rex, a duo and Marc needed a replacement for Took. Something of a character both on and off stage, Finn was often to be seen wearing a hat (including a green bowler), a trademark that was adopted by a significant proportion of T. Rex fans.
During the late 1980s and early 1990s, Finn made a handful of guest appearances with the West London rock band, Checkpoint Charlie, fronted by Mick Lexington.[citation needed]
In 1991, he joined the Croydon R&B band, WD40, which had a fluid line-up based around his old friend, drummer Stewart Childs, Colin Goody (harp, vocals), and Pete Robins (guitar, vocals). The band then added guitarists, percussionists, etc. as required, but Finn was forced to retire after about 12 months due to failing health.[citation needed] A couple of live tracks survive from this line up.[citation needed] Finn was also invited to play at the Marc Bolan 50th Anniversary gig organized by Mick Gray (ex-T. Rex tour manager and roadie), to celebrate what would have been Bolan's 50th birthday at the Cambridge Corn Exchange on 30 September 1997.
Finn died in Croydon, Surrey, on 11 January 2003, aged 55. His manager, Barry Newby commented that it was likely that Finn's illness and death were due to liver and kidney problems but it was not confirmed at the time of the interview.[1] In 2020, Finn was posthumously inducted into the Rock and Roll Hall of Fame as a member of T. Rex with Bolan, Steve Currie and Bill Legend.[4]