Mahon, Sir Bryan Thomas (1862–1930), general, was born 2 April 1862 in Belleville, Co. Galway, son of Henry Blake Mahon, landowner, and his wife Matilda, daughter of Col. Thomas Seymour, of Ballymore Castle, Co. Galway. Educated locally, he joined the 4th (Militia) Battalion of the Connaught Rangers before being commissioned into the 21st Hussars in January 1883, transferring shortly afterwards into the 8th Royal Irish Hussars. Service in India followed and he was promoted to captain (1888). He resigned his commission in 1893 to join the Egyptian army, where he took part in the campaigns against the Dervishes. He served in the Dongola expedition of 1896, was mentioned in dispatches, and was awarded a DSO. In 1897 he was promoted to major. During the reconquest of the Sudan he was present at the battles with the Mahdist forces at Atbara (April 1898) and Omdurman (September 1898) and was again mentioned in dispatches. He later served as intelligence officer of the flying column that defeated the Khalifa in Kordofan in November 1899, finishing the campaign as a brevet-colonel.
He was posted to South Africa in January 1900 following the outbreak of the second Boer war, and originally commanded the colonial mounted troops. In May 1900, with the local rank of brigadier-general, he was given command of the Mafeking relief force, of about 1,100 men. With this force he evaded the numerically superior Boers investing Mafeking, relieving the town on 17 May 1900. News of this success was greeted with wild enthusiasm in London, and Mahon was awarded a CB. In many respects the Mafeking relief campaign marked the high point of his career. In January 1901 he returned to Egypt and was appointed governor of Kordofan. Promoted to full colonel (April 1904), he then served as governor of the Belgaum district in India (1904–9). Promoted to major-general (1906), he later served as commander of the Lucknow division (1909–13).
After the outbreak of war in 1914 he took command of the 10th (Irish) Division, and it was hoped that his public image would boost recruitment despite the fact that he was both a protestant and a unionist. While there were shortfalls in recruiting, most of the division's troops were Irish by the time it was formed and fully trained in 1915, and it included several ‘First Army’ battalions. Mahon commanded the division during the failed Gallipoli campaign of March 1915 and, like the majority of generals in this affair, did not emerge with his reputation intact. In June 1915 Field-marshal Kitchener (qv) proposed that Mahon should be given command of the newly formed IX Corps. This proposal was vetoed by Gen. Sir Ian Hamilton, who described him as being ‘good up to a point and brave, but not up to running a corps out here’ (Steel & Hart, 220). Instead Hamilton appointed the elderly and indecisive Lt-gen. Sir Frederick Stopford to command the Suvla Bay landings in August 1915, under whose timid leadership the attack soon lost momentum and British troops became bogged down. Mahon found himself with less than his whole division, as his artillery was still in Egypt while more of his troops were supporting operations at ANZAC Cove. While displaying considerable caution, he recognised the strategic importance of the heights at Kiretch Tepe, directing an unsuccessful attack on this ridge on 15 August. As the whole expedition stalled, Stopford was replaced, and on 15 August 1915 Maj.-gen. Sir Beauvoir de Lisle, who was junior to Mahon, was given command of IX Corps. Mahon refused to serve under him and left for Mudros, where he remained for nine days before returning to his command. It is certain that he would have been replaced by Hamilton but for fears of protests in Ireland. While Mahon remained a popular figure with his men, his withdrawal from command at such a critical juncture in the campaign was reprehensible.
In October 1915 he transferred with his division to Salonika as part of the Allied effort to assist the Serbian army, and served as British commander-in-chief until May 1916. After a short period in Egypt, he was appointed commander-in-chief in Ireland (1916–18); the appointment was made in the hope that, as an Irishman, he could restore calm in the aftermath of the 1916 Easter rebellion. Sworn of the privy council of Ireland in 1917, Mahon displayed a sympathetic attitude to nationalist grievances but was replaced at the insistence of Lord French (qv), who was appointed as viceroy in May 1918. Mahon later served as military commander of Lille (October 1918–March 1919), retiring in 1921.
After his retirement, he returned to Ireland and married (1920) Amelia Madeline Louisa Milbanke (1876–1927), widow of Sir John Milbanke, VC, who had been killed during the Suvla Bay landings, and daughter of Lt-col. the Hon. Charles Frederick Crichton. They had no children. In 1922 Mahon became a senator of the Irish Free State, an appointment he held until his death. During his time in the senate he advocated better treatment of ex-servicemen. Despite his trying to promote a conciliatory line during the civil war, his residence at Mullaboden, Ballymore Eustace, Co. Kildare, was burned down by anti-treatyites in 1923. The house was later rebuilt. In 1927 he converted to Roman catholicism. During his career he was awarded numerous honours including the Grand Cross of the White Eagle of Serbia (1917) and the Croix de Guerre, and was created a KCB (1922) and a Grand Officer of the Legion of Honour. He devoted much of his later life to horse breeding and racing. He died 24 September 1930 at 9 Earlsfort Mansions in Dublin and was buried at Mullaboden.