Politician, lawyer and philosopher who reformed the British Army. Haldane was born in Edinburgh into a noted family, which included evangelists Robert (1764 - 1842) and James Haldane (1768 - 1851). He was the brother of respiratory physiologist John Scott Haldane (1860 - 1936), and authoress Elizabeth Haldane (1862 - 1937). Educated at the Universities of Edinburgh and Gottingen (Germany), before returning to London to study law. Haldane was called to the Bar in 1879 and appointed a Queens Counsel in 1890. In 1885 he was elected Liberal Member of Parliament for East Lothian. He helped to found the London School of Economics (1895). He served as the Gifford Lecturer at the University of St. Andrews between 1902 and 1904. He was appointed Secretary for War (1905) under the administration of Sir Henry Campbell-Bannerman (1836 - 1908). In this post he was responsible for several important reforms, including the creation of a 'General Staff' following the German model, the formation of both the Territorial Army (as a reserve) and the Expeditionary Force, which allowed Britain to prosecute the campaigns of the First World War. Haldane was raised to a peerage in 1911 as Viscount Haldane of Cloan. Appointed to the post of Lord Chancellor in 1912, he was forced to resign in 1915 having been accused of pro-German sympathies. Having joined the Labour Party in 1918, he held the same office in 1924 in the first Labour administration led by Ramsay MacDonald (1866 - 1937).
He wrote The Reign of Relativity (1921), an inquiry into the philosophical implications of the theory of relativity.
Haldane was honoured with the Freedom of the City of Edinburgh in 1912. He died at Cloan (Perth and Kinross) and is buried at Gleneagles.