Born in Castletown, County Clare, the son of Patrick O'Gorman.
He served with the Irish Brigade in the French army, and was created Chevalier by Louis XV.
O'Gorman married a daughter of Count d'Éon, and from him inherited vast vineyards, lost in the French Revolution.
After this, he retired to Ireland, where he pursued his antiquarian studies; from about 1764 he corresponded with Charles O'Conor, and had made an impressive collection of Irish manuscripts.
According to a somewhat dubious legend, O'Gorman received the Brian Boru Harp and gave it to Colonel Burton Conyngham, who transferred it in Trinity College Dublin, where it remains.