Timothy John Deasy (20 February 1839 - 18 December 1880) was an Irish survivor of the Great Famine who emigrated with his family to Massachusetts in the United States. He later became an officer in the Union Army during the American Civil War, as well as a revolutionary fighting alongside the Irish Republican Brotherhood in both Canada during the Fenian Raids and Ireland during the Fenian Rising of 1867. Towards the end of his life, he became involved in electoral politics in Massachusetts, becoming one of the few Roman Catholics elected at that time to the Massachusetts House of Representatives.