William Joseph Mellows (, 25 May 1892 – 8 December 1922) was an Irish republican and Sinn Féin politician. Born in England to an English father and Irish mother, he grew up in Ashton-under-Lyne before moving to Ireland, where he was raised in Cork, Dublin, and his mother's native Wexford. He was active with the Irish Republican Brotherhood and Irish Volunteers, and participated in the Easter Rising in County Galway, and the War of Independence. Elected as a TD to the First Dáil, he rejected the Anglo-Irish Treaty and was captured by pro-Treaty forces during the Irish Civil War. Mellows was executed by Free State forces in 1922.