Colm Kiernan was educated at Clongowes Wood College, Kildare. His father was an Irish ambassador, and Kiernan moved with the family to his father's appointments in the Holy See and Australia. Kiernan futhered his education at Melbourne and Cambridge universities and at the University of New South Wales. He subsequently worked at the University of Wollongong and was the endowed professor of Australian history at University College Dublin. Kiernan's writing included biographies of Peter Lalor, Arthur Caldwell and Daniel Mannix.
Following Kiernan's funeral, the Irish Ambassador to Australia Máirtín Ó Fainín recited the prayer 'Ár n-Athair' at Kiernan's graveside.