Born in Edinburgh, Haig studied at Brasenose College, Oxford and from 1884 at the Royal Military Academy Sandhurst. He took a commission in the 7th Queen's Own Hussars and saw service in India, in the Omdurman campaign in the Sudan and during the Boer War. Haig returned to India in 1903 as a Colonel and inspector of general cavalry. He was promoted to Major General before returning to England to a post in the War Office in 1906.
Haig helped found the British Expeditionary Force and in 1914 he was promoted to Lieutenant General and placed in command of the 1st Army Corps. Following relative successes at Mons and Ypres (1st Battle of Ypres), Haig was promoted to full General and made second-in-command of the British forces in France under Sir John French. In December 1915 Haig became Commander-in-Chief of the British forces, with French returning to Britain to head the Home forces. He directed several British campaigns, including the disastrous British offensive at the Somme, in which his side lost over 500,000 casualties while ultimately taking only few kilometers of ground, and the campaign at Passchendaele (3rd Battle of Ypres). Despite the failures, in 1917 Haig was made a Field Marshal. In 1918 following the final German assault Haig's forces had much success.
Post-war Haig became an Earl in 1919 and Baron Haig of Bemersyde in 1921. He was commander-in-chief of home forces until his retirement in 1921. He was criticised post-war for the excessive slaughter of troops under his command which earned him the nickname "Butcher" Haig.