Thesiger was educated at
Eton College before attending the
Royal Military College, Sandhurst for training as an infantry officer. Aged 21, Thesiger was gazetted into the
Rifle Brigade as a
second lieutenant on 19 March 1890, and served with his unit in England until 1898, when the regiment was dispatched to Egypt. During his service in England he was promoted to
lieutenant on 10 February 1892, and to
captain on 26 July 1897, later antedated to 26 July. In Egypt, the Rifle Brigade served on the Nile expedition under
Horatio Kitchener during the
Mahdist War and was present at the
Battle of Omdurman, which decided the campaign. Thesiger received a
brevet appointment as
major on 16 November 1898 for his service. The Rifle Brigade was then briefly stationed in
Crete during operations to maintain peace between Turkish and Greek populations on the island. In October 1899, Thesiger and the second battalion were sent for service in South Africa in the aftermath of the outbreak of the
Second Boer War. There, Thesiger saw action and was badly wounded during the battle at Wagon Hill during the
Siege of Ladysmith on 6 January 1900. He was
mentioned in dispatches for his conduct during the engagement, and received a brevet appointment as
lieutenant colonel in the South African honours list on 29 November 1900. Evacuated to Britain to recover from his wounds, Thesiger attended the
Staff College, Camberley, which he entered in January 1902 upon being seconded from his regiment and from which he graduated in late 1902. On 7 May 1902 he was appointed a
deputy-assistant adjutant-general for Musketry, and until 1906 was in charge of musketry practice on
Salisbury Plain, for the
2nd Army Corps. He was promoted to brevet colonel in November 1906. From there he moved to Ireland to work as assistant military secretary to General Sir
Neville Lyttelton, the
general officer commanding in
Dublin, a post he held from May 1908 until 1909. From there he was assigned to colonial service as the inspector general of the
King's African Rifles and in 1913 was dispatched to India as a lieutenant colonel to command the 4th Battalion of the Rifle Brigade. In 1913, in reward for his distinguished service, he was appointed a
Companion of the Order of St Michael and St George (CMG), and the following year was also made a
Companion of the Order of the Bath (CB) in the
1914 New Year Honours. In 1902, Thesiger married Frances Fremantle, daughter of General Fitzroy William Fremantle, and the couple had two children, daughter Oona Thesiger (later Buckley) and son
Gerald Thesiger, who became a notable High Court Judge and minor politician. ==First World War==