Born in Mullagh, County Cavan, McKenna's shopkeeper father, Thomas P. McKenna, was prominent in public life having held the offices of Chairman of Cavan County Council, founding Chairman of the Cavan County Board of the GAA, and a member of the Governing Body of University College Dublin (UCD).
Educated at St Patrick's College, Cavan, McKenna went on to be enrolled as a law student at UCD.
During a visit home he was arrested on 26 November 1920 and later charged with possession of ammunition and seditious materials.
[1] He was held for a time at Arbour Hill Prison he was subsequently interned at the Rath Camp in the Curragh.
After public life he continued in private practice in Kells, County Meath, until his death following a stroke on 23 July 1950.