A native of Kingscourt, County Cavan, Diarmaid began acting in student shows at DCU while studying for a business degree. He went on to study at the Gaiety School of Acting for four years.
Since graduating he has performed in the hugely successful show I, Keano (Lane Productions), as well as There Came a Gypsy Riding and Observe the Sons of Ulster Marching Towards the Somme with Livin’ Dred Theatre company. He has also appeared in An Ideal Husband, Macbeth, Christ Deliver Us and The Resistible Rise of Arturo Ui, all with the prestigious Abbey Theatre.
A fluent Irish speaker, he has tread the boards for the Aisling Ghéar Theatre’s productions of Gruaigairí and Uaigneas an Ghleanna as well as appearing in Irish language television programmes such as Seacht, Ros na Rún and Rásaí na Gaillimhe (TG4), and An Cosc, a winning entry at the 2009 Corona Fastnet Film Festival. He also regularly voices cartoons for Ireland's Irish language TV station TG4.
His other work for television includes Trivia, The Clinic and The Roaring Twenties (RTÉ), and George Gently for the BBC. In 2011 he appeared as Brastias in Starz television series, Camelot.
Diarmaid’s most recent credits include 13 Steps Down (directed by Marek Losey for ITV) ,Eoinín, a short film directed by Tom O’Sullivan, and the Abbey Theatre’s production of The Picture of Dorian Gray, in which he appeared as James Vane. One of Diarmaid’s latest roles will be portraying ‘Leif’ in the new T.V show Vikings, directed by Ciaran Donnelly, Johan Remck &Ken Girotti.
2013 has seen Diarmaid cast in The Monuments Men in the role of Captain Harpen directed by George Clooney, and co-starring Matt Damon and Cate Blanchet. He has also been cast in the new comedy series for the BBC The Wrong Mans, and Good People, to be directed by Henrik Ruben Genz.