McMenamin was born in Enniskillen, County Fermanagh, Northern Ireland, where he attended St Michael's College. He earned his B.A. from the Royal Scottish Academy of Music and Drama in 1998. He attended drama classes at Ardhowen Youth Theatre before moving on to work with the Ulster Youth Theatre.
McMenamin has appeared on various BBC and ITV programmes, including "4:50 From Paddington", an episode of Agatha Christie's Marple, starring Geraldine McEwan, in which he played Cedric Crackenthorpe, and in the Channel 4 comedy series The Young Person's Guide To Becoming A Rock Star. In 1999 he was cast in the title role of the BBC1 television movie David Copperfield. He co-starred in The Golden Hour (ITV, 2005), playing a doctor.
In January 2009, he appeared in a one-off special episode ("The Grinning Man") of the BBC's Jonathan Creek, playing a grounds keeper. He co-starred in the 2001 movie To End All Wars. In 2008, he played the lead role in The Last Confession of Alexander Pearce. In 2011, he played the role of Matt Anderson on the science fiction television programme Primeval.
|Rab C. Nesbitt||Young Man||TV series (1 episode: "Property")|
|The Young Person's Guide to Becoming a Rock Star||Jez MacAllister||TV series (6 episodes)|
|1999||A Rap at the Door||Dermot Millen|
|The Trench||Pte. Charlie Ambrose|
|David Copperfield||David Copperfield||TV movie|
|The Last Minute||Garvey|
|To End All Wars||Capt. Ernest 'Ernie' Gordon|
|2002||Sunday||Leo Young||TV movie|
|Any Time Now||Johnny Doherty||TV series (4 episodes)|
Nominated—IFTA Award for Best Actor in a TV Drama
|Weird Nature||Narrator||Six-part nature documentary on the BBC and Discovery Channel|
|Birthday Girl||Donal||TV movie|
|2003||Lena: The Bride of Ice|
|Watermelon||Adam Collins||TV movie|
|Strange||Liam||TV series (1 episode: "Costa Burra")|
|The Private Life of Samuel Pepys||Will Hewer||TV movie|
|2004||Pulling Moves||Tomas 'Ta' McKeown||TV series (10 episodes)|
|Agatha Christie's Marple||Cedric Crackenthorpe||4.50 from Paddington|
|Silent Witness||Joe Galvin||TV series (2 episodes: "A Time to Heal")|
|2005||Jericho||D.C. John Caldicott||TV series (4 episodes)|
|The Golden Hour||Dr. Paul Keane||TV series (4 episodes)|
|2007||True Dare Kiss||Bryce Waghorn||TV series (6 episodes)|
|2008||Messiah: The Rapture||Daniel Hughes||TV movie|
|The Fixer||Scott Glover||TV series (1 episode: "Episode #1.4")|
|Silent Witness||Rhys Allen||TV series (2 episodes)|
|The Last Confession of Alexander Pearce||Alexander Pearce|
|2009||Jonathan Creek||Glen||TV series (1 episode: "The Grinning Man")|
|Demons||Quincey||TV series (1 episode: "Suckers")|
|One Hundred Mornings||Jonathan|
|2011||Primeval||Matt Anderson||TV series (13 episodes)|
|The Sinking of the Laconia||Declan McDermott||TV mini-series (2 episodes)|
|32 Brinkburn Road||Sid||TV mini-series (4 episodes)|
|2012||Saving the Titanic||Frederick Barrett||TV movie|
|Lewis||Nick Addams||TV series (S6:E3 "Fearful Symmetry")|
|2013||Made in Belfast||Jack Kelly||Theater|
|2014||Death in Paradise||Dan Parish||TV series (1 episode: "Episode #3.6")|
|Land Is God||Seamus||short|
|Shooting for Socrates||Sammy McIlroy|
|2015||Rapt||Jonathan||TV mini-series (3 episodes)|
|Midsomer Murders||Craig Coffley||TV series (1 episode: "Habeas Corpus")|
|2017||Paula||McGlynn||TV mini-series (2 episodes)|
|2018||The Convent||William Carpenter|
|Grace & Goliath||Marcus|
|2020||Rig 45||Trevor||TV series (6 episodes)|
- "Interview with Ciarán McMenamin". Enniskillen Town United Football Club. Archived from the original on 29 August 2018. Retrieved 14 July 2016.
- "Ciarán McMenamin webpage". Archived from the original on 2 March 2001. Retrieved 3 July 2019.
- "Masterpiece Theatre - David Copperfield". PBS. Retrieved 18 October 2011.
- Andrew Johnston (4 April 2012). "Film Review: Saving the Titanic". CultureNorthernIreland.
- Ciarán McMenamin at IMDb
- Brouwer, Julian (2008). "HE'S S-CIARAN THEM TO DEATH; Irish star bares all as deranged cannibal on run". Retrieved 18 October 2011.