Mick began his acting career with Taibhdhearc na Gaillimhe (Ireland's national Irish language theatre), and was a founding member of the Druid Theatre Company. Lally received an Irish Times/ESB Theatre Award Nomination for Best Actor for his role in Druid's production of "The Dead School". Lally also became a member of the Field Day Theatre Company, and starred in the company's 1980 premiere of Brian Friel's play "Translations". He first played at the Abbey Theatre in 1977 in a production of "Wild Oats" and went on to perform in many other Abbey productions.