BGen Irwin was born in Sackville, New Brunswick. His father was an officer in the RCAF and he, therefore, attended schools in England, Ottawa and Toronto. He entered the Royal Military College of Canada in 1969 and graduated in 1973 with a Bachelor of Engineering (Mechanical) degree.

In October 1973, he joined 3 Field Squadron in Chilliwack. While there he was appointed to several positions within the unit, one of which was Project Commander for construction of the Eagle River Bridge in the northern Yukon Territory from July 76 to July 77. He was subsequently awarded the Chief of Defence Staff Commendation for leadership qualities exhibited during this project. He was then posted to CFB Borden for employment in the Construction Engineering Section as Engineering Officer and Production Officer. In 1980, he served on the Golan Heights in the Middle East with the United Nations Disengagement Observer Force (UNDOF).

In August 1980, upon promotion to Major, BGen Irwin served as Staff Officer, Grade 2 Technical Services, in Headquarters Combat Training Centre at CFB Gagetown. He was then selected to attend the Canadian Forces Command and Staff College in Toronto. He was appointed Commanding Officer, 4 Combat Engineer Regiment, Lahr, Germany in 1984.

BGen Irwin was promoted to LCol in 1986. He returned to Canada to NDHQ where, for two years, he assumed the appointment of Chief of Construction and Properties Coordinator. Between August 1988 and June 1989, he attended continuous French Language Training and was then appointed Commandant, Canadian Forces School of Military Engineering in Chilliwack, BC. In 1992, he served with the United Nations in the former Yugoslavia as Force Engineer and, upon promotion to Colonel, as Commander of the Canadian Contingent. Upon his return to Canada, he was appointed as Director Construction Engineering Requirements and shortly after, as Director General Infrastructure. In Jul 96 he was posted to the Army staff as G3 and later as Director Land Force Readiness and J3 Land.

In 1999, BGen Irwin was appointed as the Canadian Forces Military Attaché at the Canadian Embassy in Washington DC. He was promoted to his current rank in 2001, and appointed Director General Military Engineering/J3 Engineers at NDHQ, and in 2005 he was appointed CEO of the Canadian Forces Housing Agency/J3 Engineers.

BGen Irwin retired from the Canadian Armed Forces in July 2005. For the following six months he continued as CEO of CFHA. In 2006 he joined Defence Construction Canada as Vice-President Operations. In 2011, he retired from DCC and, since then, has been consulting with CFN Consultants. On 3 December 2014, the Minister of National Defence approved the appointment of BGen Irwin as the 13th Colonel Commandant of the Canadian Military Engineering Branch.