Geoghegan was admitted as a
solicitor at the age of 21 and practised in
County Cavan and
County Monaghan. Relinquishing the solicitor side of the profession, he was
called to the Bar of Ireland on 1 November 1915 and to the Bar of England in 1923. He practised successfully as
junior counsel before becoming a
senior counsel in 1925. Geoghegan had been a pro-Treaty Redmondite and had joined
Cumann na nGaedheal in the early 1920s. He came into contact with
Fianna Fáil when he was among those advising
Éamon de Valera on the payment of land annuities, and in 1930, he joined that party. He was elected to
Dáil Éireann in a
by-election on 13 June 1930 as a Fianna Fáil
TD for
Longford–Westmeath. When Fianna Fáil took office in March 1932, he was appointed
Minister for Justice. This was a sensitive post, coming in the first change of government since the Civil War. As well as being fitted by his legal expertise, the choice of Geoghegan, with his Cumann na nGaedheal background, offered the opposition reassurance as to de Valera's intentions. The historian Dónall Ó Drisceoil has suggested that Geoghegan's position as a
Knight of Saint Columbanus was why he gave into Catholic Church pressure to deport the "communist" Gralton. serving for less than two months. In his brief tenure, he assisted the government in the preparation and enactment of the
External Relations Act on 12 December 1936, before being appointed a judge of the
Supreme Court on 22 December 1936, vacating his seat in the Dáil. Geoghegan remained on the bench of the Supreme Court until his retirement due to ill health in April 1950. His son,
Hugh Geoghegan enjoyed the distinction in 2000 of being the first appointee to Ireland's Supreme Court to follow in his father's footsteps. ==Later life and death==