Brennan, Garrett (Gerald Brennan/O'Brennan; Gearóid Ó Braonáin/ Ó Breanáin) (1894–1974), revolutionary and garda, was born 7 October 1894 in Castlecomer, Co. Kilkenny, second of ten children of Cornelius Barrett, shopkeeper, and Margaret Brennan (née Boran). One of his brothers was Martin Brennan, the first professor of education at St Patrick's College, Maynooth, Co. Kildare. Educated at St Kieran's College, where he was ostracised for favouring GAA over rugby, and Knockbeg College, Carlow, he studied medicine at UCD from 1912 before becoming a wireless operator on a British merchant navy troopship during the first world war. Arrested and imprisoned for welcoming the news of the 1916 rising on a postcard to his family, he returned to Ireland at the end of the war and joined D Coy, 3rd Bn (Castlecomer), North Kilkenny Brigade IRA, rising to the rank of commandant in July 1921. At the urging of Kevin O'Higgins (qv) he joined the national army and held the rank of brigade quartermaster. In October 1922 he joined the civic guard with the rank of superintendent and was stationed at Lady's Lane, Waterford (October 1922–September 1923). Promoted to chief superintendent in July 1923, he was stationed in Ennis (September 1923–December 1924), Cork city (December 1924–March 1929), and Dublin castle (March 1929–March 1933). In March 1933 he was transferred to the crime and security section of the detective branch at garda headquarters, Phoenix Park, and remained with the detective branch till 1936. There he took charge of the team that investigated the Ball murder case (1936) (see Edward Preston Ball (qv)) and organised the new Garda Technical Bureau, where under his direction forensic science was introduced into criminal investigations. In August 1936 he was promoted to assistant commissioner and took charge of the traffic section. Assigned to Dublin castle (1938–47), he was appointed deputy commissioner in December 1939 and returned to the crime branch in May 1947, where he remained till his retirement on 6 October 1959. Chairman of the Garda Joint Representative Body, he was a founding member and later president of the garda branch of the St Joseph's Young Priests Society (1945–59); he was also president (1957–63) and vice-president (1974–6) of the national society. He married (24 March 1924) Elizabeth Cecilia Dwyer (d. 1980) of the Square, Castlecomer; they had seven children. The family lived at Eaton Square, Monkstown, Dublin, from 1936. He died 18 February 1974 in Dublin, leaving an estate valued at £13, 244.
Ir. Press, 19 Feb. 1974; Conor Brady, Guardians of the peace (1974); The Sheaf (summer 1974), 10; James J. Comerford, My Kilkenny IRA days 1916–22 (1978); Tom Lyng, Castlecomer connections (1984); Jim Maher, The flying column: West Kilkenny 1916–21 (1987); Liam McNiffe, A history of the Garda Síochána (1997); information from Mr Louis Brennan (son) and garda archives