William Oge Martyn, or William Oge Martyn fitz Thomas, fl. 1566-1592, was a son of Thomas Oge Martin and Evelina Lynch of Galway. Bailiff of Galway in 1566 to 1567, kidnapped by the Earl of Thormond in January 1570, he fought at the battle of Shrule in April of the same year. He served as High Sheriff of County Galway and Jailer of Athlone Castle during the 1570s and 1580s.

Martyn attempted to capture or kill the pirate Grace O'Malley at her stronghold of Rockfleet in 1579, but was repulsed. In 1580 he personally hanged William Burke, third son of the 2nd Earl of Clanricarde , for rebellion at the gallows outside the walls of Galway, despite knowing that he had being pardoned.

Martyn served as Mayor of Galway from September 1586 to September 1587. He also served as a negotiator 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. He was survived by his brother, Francis, sons John and Richard. and was the ancestor of Edward Martyn of Tullira Castle (1859-1923).