Lucas obtained the command of an English troop in the Dutch service, and was knighted by Charles I on 14 April 1628. In December 1638 Thomas Wentworth, 1st Earl of Strafford gave him the command of a troop in the Irish army. He was one of the officers in whom Ormonde most confided during the Irish Rebellion of 1641, and held the rank of commissary-general of the horse. He distinguished himself at the Battle of Kilrush (15 April 1642), and was badly wounded at the Battle of New Ross on 18 March 1643.