 He was made adjutant of the 1st Battalion on 22 May 1694 and promoted to captain on 2 October 1695, when serving with the regiment before Namur; his commission was renewed in 1702.In 1704 he was wounded at the Battle of Schellenberg, and he was promoted to major on 3 August that year.Irwin served as a brigade-major at the Battle of Blenheim, where he was again wounded, and was later present at Ramillies and Malplaquet.