Sullivan served with the West Yorkshire Regiment during World War I, returning to the clothing industry after the war. In 1920, when the National Union of Tailors and Garment Workers was formed, he was appointed as its full-time London District Secretary. He also served on the Shirt, Collar and Tie Wages Council, the Wholesale Tailoring Wages Council, the Made Up Textile Wages Council, and the Regional Board for Industry,[2] and was a member of the London Trades Council.[1]
Initially, Sullivan was seen as one of the more radical figures in the union, a member of the Friends of Soviet Russia,[3] and a supporter of striking workers at Rego in 1928. Unlike the London District Organiser Sam Elsbury, he did not join the United Clothing Workers' Union split.[4] During the Spanish Civil War, he supported the republicans. A founder of the Association of Catholic Trade Unionists, and a leading figure in the Catholic Action movement, and was prominent in arguing the case for Catholic schooling during debates around the Education Act 1944.[2]