Career
He was also a strong supporter of home rule for Scotland, a minimum wage and the Temperance movement. He was originally a Liberal but then joined the Independent Labour Party. He was Chairman of the Select Committee on Capital Punishment, 1929–1930 which reported at the end of the latter year.
In 1930-1931 he 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.
Barr was the grandfather of James Barr (biblical scholar).