He wrote for radical and socialist newspapers. From 1911 until 1915, Curtin was employed as state secretary of the Timberworkers' Union. He was elected federal president of the union in 1914. During World War I he was a militant anti-conscriptionist; he was briefly imprisoned in December 1916 for refusing to attend a compulsory medical examination, even though he knew he would fail the exam due to his very poor eyesight. He also stood (unsuccessfully) as the Labor candidate for Balaclava in the 1914 federal election. The strain of this period led him to drink heavily and regularly, a vice which blighted his career for many years. He proposed to Elsie Needham, the sister of Labor Senator Ted Needham, on St Kilda Beach, and they were married on 21 April 1917 in the dining room of a private home in West Leederville.