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.
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.
[4] 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.
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.