He was born in Shelburne, Nova Scotia, the son of Robert Gore Irwin and Isabel Archer, and was educated there. Irwin worked for fifteen years as a travelling salesman before establishing a lumber and dry goods business at Shelburne. In 1894, he married Mary Prescott McGill. Irwin was speaker for the provincial assembly from 1917 to 1925. He died in Shelburne. His brother Harry Irwin was Hawaii Attorney General and a judge in Hawaii. His brother Fred was a physician and surgeon in Hawaii. They also had a brother named Archer.