Swift was active on the Dublin Trades Council, succeeding Larkin as president in 1945, and becoming editor of "Workers' Action", its newspaper. He served as president of the Irish Trades Union Congress in 1946, using his presidency to promote workers' education; this led to the founding of The People's College. He was also prominent in the International Union of Food and Allied Workers' Association, working with Herman Leuenberger to maintain unofficial contacts with trade unionists across Europe during World War II, and to assist refugees, and he served as president of the international from 1964. Swift was a member of the Labour Party from 1927, always associated with its left-wing. He wrote the party's "Workers' Democracy" policy in the 1960s. In 1973, he surprised many by supporting Ireland joining the European Economic Community. Swift retired from his trade union posts in 1967 and wrote a history of the Irish Bakers. In retirement, he served as president of the Irish Labour History Society, and also as president of the Soviet-Ireland Society.