Brendan Gleeson studied English and Irish at University College Dublin, then taught secondary school while acting in semi-professional and professional theatre in Dublin and surroundings. He joined the Dublin-based Passion Machine Theatre Company, where he acted in early plays and also wrote and directed productions. At age 34 he left teaching to commit full-time to acting. His mediums include stage, television, voice (animation), and film. He has collaborated with playwrights such as Paul Mercier, and with directors including Martin McDonagh. His working methods include developing roles through theatre and workshops, shifting between ensemble and leading parts, performing voice roles in animation, and balancing screen and stage work. Over time his career evolved from Dublin theatre into international screen projects, maintaining connections with Irish theatre and folklore in voice and musical contributions.