Bailiff of Galway in 1566 to 1567, he was kidnapped by the Earl of Thomond in January 1570 but was free in time to participate at the battle of Shrule in April of the same year.
In 1580 he personally hanged, among others, William Burke, third son of the Earl of Clanricarde, for rebellion at the gallows outside the walls of Galway, fully aware that the condemned men had been pardoned.
And after the Earl's son went in, William Martin and the Saxons acted treacherously towards him; and they apprehended himself; and nine of his people were hanged, and he himself was put in prison, in despite of the mayor, and of the town.
He participated in a notorious session in December 1586, as recorded in the Annals of the Four Masters: A session was held at Galway in the month of December of this year, and many women and men were put to death at it; and Edmond Oge, the son of Edmond, son of Manus Mac Sheehy, and eight soldiers of the Geraldines along with him, were put to death, information having been given against them that they had been along with those Scots who were slain at Ardnarea.
William Óge also served as an interlocutor between the O'Flaherty's of Connemara and the administration in Dublin Castle in 1585 and 1586, and again in 1589 and 1590, when they rose in rebellion.