Moraghan was born in Toxteth, Liverpool on 27 January 1963. He started acting in 1978, when the BBC held auditions in his high school for the TV play Lies, and he was selected. On 14 May 1988, Moraghan started his professional acting career playing a ferryman in the comedy Help!, and he subsequently went on to play in many TV series and several films. His longest running role was Owen Davies, a Consultant Obstetrician, in Holby City which he played from 2001 until 2005. He also appeared in a television commercial for the fabric softener 'Bounce' in 1996 with fellow Liverpudlian Katy Carmichael. He was recently a member of the cast of the British independent film Allies (2014).
He performed as a backing vocalist and percussionist in the Liverpool band Personal Column in the late 1970s. In 2006, Moraghan came second in the BBC singing competition Just the Two of Us. His singing partner was Atomic Kitten singer Natasha Hamilton with whom he sang classic songs like "Islands in the Stream" and "With You I'm Born Again". He has also appeared on Lily Savage's Blankety Blank.
Moraghan may be best known for his acting, but he also sings and in 2006 he starred in a musical production of Willy Russell's "Our Day Out" at Liverpool's Royal Court Theatre.
In 2008, Moraghan appeared in Celebrity MasterChef, reaching the final alongside Andi Peters and eventual champion Liz McClarnon.
Moraghan's swing album, Moonlight's Back In Style (words by Nicky Campbell) was released on Linn Records on 14 September 2009. He sang the title song from the album on GMTV on 2 September 2009.
From 2013, Moraghan became the narrator on the children's television show Thomas & Friends, succeeding both Michael Brandon and Michael Angelis (for both the US and the UK, respectively). He is also narrator for the Thomas & Friends specials/films, King of the Railway, Tale of the Brave, The Adventure Begins, Sodor's Legend of the Lost Treasure, The Great Race and Journey Beyond Sodor.
December 2017 Mark is starring in Jack and the Beanstalk Pantomime in Bournemouth where he plays the devilish Fleshcreep.
