Son of Free Church Minister John Baillie, he was born in the Free Church Manse in Gairloch, Wester Ross, on 26 March 1886. A leading theologian, he held academic posts in the UK, USA and Canada. His brother Donald Macpherson Baillie was Professor of Systematic Theology at the University of St. Andrews and his other brother Peter Baillie served as a missionary doctor at Jalna, India.
He met Florence Jewel Fowler while he was in France during the First World War. They married at Leamington Spa in 1919. Their only child, Ian Fowler Baillie, was born in 1921.
Baillie wrote A Diary of Private Prayer (1936), regarded as a devotional classic. But his most important contribution to theology was an exploration of the relationship between the knowledge of God to spiritual and moral experience.
As Convener of the Church of Scotland's General Assembly's "Commission for the Interpretation of God's Will in the Present Crisis" ("The Baillie Commission"), reporting to the Assembly 1941 to 1945, Baillie helped the Church to think through its approach and mission to the post-war world.
^Secretariat for Evangelism (1954) Ecumenical Studies: Evangelism in Scotland Geneva: The World Council of Churches p.55; John Baillie, 'Preface' (1945) God's Will for Church and Nation London: SCM Press, pp.7-8.
Nigel M. de S. et al., Dictionary of Scottish Church History and Theology, pp. 693–698. T & T Clark, Edinburgh 1993. ISBN 0-567-09650-5
John McIntyre, Foreword, in John Baillie, "The Sense of the Presence of God", Oxford University Press, 1962
George Newlands, "John and Donald Baillie" in Blackie, Nansie (2005) A Time for Trumpets: Scottish Church movers and shakers of the twentieth century Edinburgh: Saint Andrew Press pp.17-28.