In 1883, Birkbeek was commissioned as a lieutenant in the 1st King's Dragoon Guards, then sent to India. He served in the Hazara Expedition of 1888 and Chin Lushai Expedition of 1889-90 as a signalling officer. He was mentioned in despatches and received the campaign medal and two clasps, and was promoted to captain on 31 January 1890. He became aide-de-camp to Major-General Henry Clement Wilkinson, commanding the North-Eastern District at York, while he prepared for entrance to Staff College, Camberley. He was in the famous 1896-97 class at Staff College that included Douglas Haig, 1st Earl Haig and Edmund Allenby, 1st Viscount Allenby, and many other officers who distinguished themselves in the Second Boer War and First World War, and was promoted to major on 3 April 1897. Birkbeck served throughout the Second Boer War in South Africa as assistant Inspector of Remounts and received the brevet promotion to lieutenant-colonel on 29 November 1900. He impressed his superiors, the Commander-in-Chief in South Africa, Lord Kitchener, referred to him in a despatch as "perturbed by nothing" and with "considerable ability". For his service in the war he was created a Companion of the Order of the Bath in the October 1902 South Africa Honours list. Following the war, he served with the War Office for two year as a Staff officer with military education and training under Field-Marshal Sir Henry Wilson, who became one of his closest friends. In 1905, he was posted for a year with the Japanese Army in Manchuria, "where his immense size and genial nature made an excellent impression on our Allies, and led them to help him with much valuable information for his reports." After returning home, he spent several years as commander of the Cavalry School, on Netheravon. In 1912, he returned to the remount service, and served as its director with the War Office from 1912 to 1920.
Personal life
In 1905, he married American Mabel, of New Brighton, Staten Island. They had three sons. In 1915, he suffered a fall from his horse and was injured, and never fully recovered. He died after a fall while hiking at St. Briac, near Dinard in France in 1929.
