Evangelist and writer. Born in London into a Scottish family, Haldane was the elder brother of another evangelist, James Haldane (1768 - 1851).
Haldane was educated in Dundee and Edinburgh before attending the University of Edinburgh. He joined the navy at 16, serving briefly with his uncle Admiral Adam Duncan (1731 - 1804). However, Haldane left the navy in 1783, having taken part in the relief of Gibraltar (1782). He undertook a 'Grand Tour' in Europe, married (1786) and then settled at his family seat, Airthrey Castle (Stirling).
However, he developed an evangelical zeal and, in 1797, he sold the castle, left the Church of Scotland and toured Scotland preaching. With his brother he founded The Society for Propagating the Gospel at Home, which gave the impetus for the development of the Congregational Churches.
He proceeded to plan missionary work and adopted Baptist principles. He taught theology at the University in Geneva (1816) and Montauban (1817), and published widely on evangelical themes. Returning to Scotland (1819), he purchased a new estate at Auchengray (South Lanarkshire).
He died in Walker Street, Edinburgh and is buried in Glasgow Cathedral.