This thesis documents the theatre work of Walter Macken and establishes his contribution to Irish theatre as a playwright, actor and theatre manager. The work also provides a view o f theatre in mid-twentieth century Ireland. The research examines his working life as an actor from 1933 when he joined Taibhdhearc na Gaillimhe to his performance in film in 1962. The quality of his performances is examined, based on contemporary reviews by theatre critics and others. It is shown that Macken was an actor within the Irish realistic tradition. He wrote his first play in the mid-1930s and had a total of 35 titles to his name before his early death in 1967. If we exclude all but his conventional plays, his unfinished musical, God's Own Country, and Recall the Years, scripted for the opening o f the new Abbey Theatre in 1966, his total output is 21 plays including short plays. Each of the 21 plays is evaluated and discussed in detail, in order to clarify the range and variety o f M acken’s dramatic imagination, heretofore too often seen as limited. While the novels and short stories do not form the subject of this thesis, it will be shown that the plays are often based upon or relate to the fiction in theme, plot and/ or characterisation. The quality of his performed plays is discussed in the light of criticism by theatre critics writing at the time and the later opinions of other writers on mid-twentieth century Irish playwrights. Macken spent from 1939 until 1948 as manager of Taibhdhearc na Gaillimhe. He was the second government nominee on the Abbey Board from 1965 until 1966. During this time he was appointed to the positions of assistant manager and artistic adviser and held all three positions until his unexpected resignation in June 1966. The thesis concludes that as an actor Walter Macken was as much an artist as when he wrote plays or novels. As a playwright he has been seriously underrated and the range of his work under appreciated and in need of re-interpretation.