1900 Jan 1. Born Dublin. His father was a barrister and his mother was an editor on the Freemans Journal; his aunt, Katherine Tynan, a famous writer. He had two younger brothers; John Michael Finbar and Donal J Patrick O'Mahony. He was baptised "Gerard John Cullen O'Mahony" and appears to have added the "Tynan" later in life - his officers record includes the "Tynan".
1901 census at Tallagh, Dublin
1904 Nov 28. His father died
1911 census at Tallagh, Dublin
He was educated at St Mary's College, at the Catholic University School and at Claude Fulcher's Military Academy ( a school designed to instruct pupils on the exams to enter RMA Woolwich).
1918 Oct 30. Commissioned into the Royal Irish Regiment as 2nd Lieutenant from Dublin University O.T.C. and subsequently served in Egypt.
When he returned to civilian life he was employed for a time by the Ministry of Labour
1921 Jan 19. Joined the ADRIC with service no. 1574. Posted to N Coy
According to the journalist Hugh Oram he had lost a leg earlier in life and had to wear a wooden leg. According to one story he would go to a fancy dress party dressed as a toffee apple.
1921 Aug 30. Witness to a robbery
Fines of £2, £2 and 10/- from Coy Commander
1922 Jan 14. Discharged on the demobilisation of ADRIC
1922 Mar 29. Joined the British Gendarmerie section of the Palestine Police as a Constable
After leaving the Gendarmerie, he was responsible, along with another officer ( Major James Munro), for the defence plans of the newly constituted Jewish colonies in Galilee and Phoenicia, as well as for the early construction work on the trunk road across the Judean Hills, linking Samaria and Jaffa.
1925 he returned from the Near East and joined the commercial staff of the Daily News in London. Later he worked with the advertising and news departments of the Daily Express.
1928 He joined the Irish Times as art editor, and subsequently occupied positions in the editorial, advertising, circulation and commercial departments. He became Assistant Manager, and on the death of the late Mr John O'Dockery he was appointed Manager.
1929 Oct/Dec. Married in London to Jean Ballantyne Archer. They had three children
1936 Jul 6. Born at Merrion House, Lower Fitzwilliam Street, Dublin, the youngest son David Edward John Archer Cullen Tynan-O'Mahony was better known as Dave Allen the comedian. He was brought up in Ireland as a Roman Catholic by a mother who was a converted Anglican and a father who was an agnostic. A biography of Allen says that his childhood became impoverished after his father took to drink and gambling. His father died when David was twelve. No longer well dressed, the boy went to Terenure College, Dublin, but the loss of his father affected him profoundly.
1948 Apr 17. He died at his home in Dublin. The Irish Times naturally ran an obituary, which stated that O'Mahony was manager of the Irish Times from 1942 until he resigned, because of prolonged ill-health, a few months before his death.