He was born on 26 July 1862 at Beanscroft Farm near Fenwick, East Ayrshire the son of Allan Barr a farmer and his wife Elizabeth Brown.[2][3]
He studied a general degree at Glasgow University graduating MA in 1884. He returned to university around 1889 to study Divinity, graduating BD in 1892.[4]
He was ordained as a minister of the Free Church of Scotland in 1889 serving Johnstone and Wamphray. In 1895 he became minister of Dennistoun in east Glasgow.
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 Presbyterianminister, 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. In 1929, the year that the remainder of the United Free Church merged with the Church of Scotland, he was the first Moderator of the General Assembly of the United Free Church of Scotland Continuing, the section which refused to merge with the Church of Scotland.[5]
In 1890 he married Martha Wilson Stephen.[6] They had five children including their last child who was the minister Elizabeth Barr. She was first woman in Scotland to be a Presbyterian minister.[7]
Great Britain. Parliament. House of Commons. Select Committee on Capital Punishment.; Rev. James Barr (Chairman) (1931). Report from the Select Committee on Capital Punishment : together with the proceedings of the Committee, and the minutes of evidence, taken before the Select Committee on Capital Punishment in 1929-1930, together with appendices and index. London: HMSO. cxiv, 681 pp.