Sir Thomas Cusack (also spelt Cusacke or Cusake) (1490–1571) was an Anglo-Irish judge and statesman of the sixteenth century, who held the offices of Master of the Rolls in Ireland, Lord Chancellor of Ireland, and Chancellor of the Exchequer of Ireland, and sat in the Irish House of Commons. He was one of the most trusted and dependable Crown servants of his time, although he led a somewhat turbulent private life.
He was an ancestor of the Duke of Wellington. He is also memorable as the fourth of the six husbands of Jenet Sarsfield, who was his third wife.