After securing a militia commission in the 4th Battalion Royal Scots Fusiliers in 1883, Birdwood trained at the Royal Military College, Sandhurst, from which he was commissioned early, owing to the Russian war scare of 1885, becoming a lieutenant in the 12th (Prince of Wales's) Royal Lancers on 9 May 1885. He joined his regiment in India and then transferred from the 12th Royal Lancers to the Bengal Staff Corps on 20 December 1886. He subsequently transferred to the 11th Bengal Lancers in 1887, seeing action on the North-West Frontier in 1891. He later became adjutant of the Viceroy's Bodyguard in 1893. He was promoted to captain on 9 May 1896 and saw action during the Tirah Campaign in 1897.