John Baillie was born in 1886, the son of Rev John Baillie ( 1829-1891), Free Church minister at Gairloch, Ross & Cromarty in the north-west of Scotland, and his wife Annie Macpherson. John (senior) was a graduate of both the University of Edinburgh and Free Church College, Edinburgh

Following the death of his father in 1891, the family home was at Inverness and John (junior) was educated at Inverness Royal Academy and the University of Edinburgh. More study was undertaken at both the universities of Jena and Marburg and he held assistant positions at the University of Edinburgh before entering the church, as an assistant in 1912 and then being ordained in 1920.

The First World War saw Baillie playing an active role in both the YMCA and the British Expeditionary Force. The end of that war saw his marriage to Florence Jewel Fowler and the start of his academic career. He held a number of chairs at the Auburn and Union Theological Seminaries, New York, and at Emmanuel College, Toronto, but he eventually returned to Edinburgh to become Professor of Divinity at New College in 1934. The advent of the Second World War saw Baillie use the North American links he had maintained to help persuade US entry into the conflict. He was elected as Moderator of the General Assembly of the Church of Scotland and became Dean of the Faculty of Divinity at Edinburgh in 1950, holding this position until retrial six years later. As part of the ecumenical movement, John Baillie was member of both the British Council of Churches and the World Council of Churches; he became a President of the latter.

John Baillie's brother, Donald Macpherson Baillie ( 1887-1954) was educated at Inverness Royal Academy and at the Universities of Edinburgh, Marburg and Heidelberg. He graduated with an MA from New College Edinburgh in 1909, and he spent some time with the YMCA in France before being ordained in 1918 and was minister of Bervie United Free Church until 1923. Moving to St. John's, Cupar he was there until 1930 and then at St. Columba's, Kilmacolm until 1934.

Donald was appointed Kerr lecturer at the University of Glasgow in 1923, delivering lectures in 1926. In 1935 he became Professor of Systematic Theology at the University of St Andrews, where he had been Additional examiner for the BD degree in Divinity and Ecclesiastical History from 1921-1924, and which had awarded him an Honorary DD in 1933. Other academic positions included External Examiner for the BD in Divinity at the University of Edinburgh from 1933, Forwood lecturer in the Philosophy of Religion at the University of Liverpool, 1947, and Moore lecturer at the San Francisco Theological Seminary, 1952.

John and Donald's brother, Peter Baillie ( 1889-1914), was educated at Inverness Royal Academy and then at George Watson's College. Entering Edinburgh University in 1907, he graduated with a M.B., Ch.B. in 1912. For many years he was a member of the Philomathic Society and became its President in 1911. He was senior house surgeon at Mildmay Mission Hospital, London, for six months and in January 1914 he left Britain for Jalna, India, taking up a post to which he had been appointed by the Foreign Mission Committee of the United Free Church. He was ordained as a missionary elder of Langside Hill United Free Church, Glasgow, prior to his departure. While in India he was the victim of a drowning at Mahableshwar.