 Byrne participated in preparations for the 1798 Rebellion, fought at Oulart, Enniscorthy, the "Battle of Clough" (or "Battle of Tubberneering"), the Battle of Arklow, the Battle of Vinegar Hill, Castlecomer and Ballygullen at the age of 18.After the Wexford Rebellion was over, he joined Michael Dwyer and Joseph Holt in the Wicklow Hills, continuing to fight on.Next he settled in Dublin.