 In 1930–1931, Barr was Chairman of the Liaison Committee, as the Chairman of the Parliamentary Labour Party was then known at any time when the party was in government.A Presbyterian minister, Barr strongly opposed any link between church and state; in his view, the Church must support and maintain itself on an entirely voluntary basis.For this reason, he was a prominent member of the United Free Church of Scotland and he led the opposition to that group's reunion with the Church of Scotland in 1929; he and those of like mind did not participate in the reunion and continued as the United Free Church of Scotland, which is still in existence.