During the War of the Two Kings he was given command of a newly raised infantry regiment in the Irish Army which took part in an expedition led by Patrick Sarsfield to capture the Protestant-held town of Sligo.
[2] In 1690 O'Gara commanded the Jacobite garrison at Jamestown in County Leitrim, repulsing an advance by a much larger force of Williamite troops under James Douglas.
[6] In 1727 the exiled James III awarded him a baronetcy and he was styled by the Jacobites as Sir Oliver O'Gara, but this was never recognised by the Irish government in Dublin.
She was the widow of Richard Fleming Esq of County Meath and had a daughter named Bridget by that union.
[7] His eldest son John Patrick O'Gara rose to the rank of Brigadier in the Spanish service.