Colgan was educated at Saint Patrick's Grammar School, Armagh and Corpus Christi College, Oxford, where he read English.
He studied at l'École Internationale de Théâtre Jacques Lecoq in Paris and has lived in London.
He also spent a year working in the Abbey Theatre in Dublin and has appeared in several television productions, including Rebel Heart and Sunday (2002) for the BBC.
In 2009 he was appearing at the Young Vic in Rupert Goold's critically acclaimed production of King Lear starring Pete Postlethwaite.
[5] The second was HBO's 2019 mini-series Chernobyl in which he depicts Soviet Minister of Coal Industry Mikhail Shchadov.