Byrne, Sir William Patrick (1859–1935), under secretary for Ireland (1916–18), was born 12 February 1859 at Beech House, Withington, Lancashire, the fourth son of John Byrne. After attending at St Cuthbert's College, Ushaw, and St Bede's College, Manchester, he studied law at the University of London, graduating BA (1882). Called to the bar (1886), he became a bencher at Gray's Inn in 1908. He joined the civil service as a clerk at the GPO in 1881, transferred to the Home Office staff in 1884, and later served as private secretary to the permanent under secretary of state (1891–5) and to the secretary of state (1895). He worked on numerous home office committees including those on judicial statistics (1892) and riots (1894), and was made senior clerk at the Home Office in 1896 and principal clerk (1898–1908). In 1908 he became assistant under secretary at the Home Office and visited Paris in 1910 as the British delegate to the international conference on aerial navigation. The treatment and care of the insane was of particular concern to him and he became chairman of the board of control for lunacy (1913–19). He was created CB (1902) and KCVO (1911).
In May 1916 he was sent to Ireland as a member of the Sankey commission investigating the involvement of civil servants in the Easter Rising. It recommended that all government employees implicated in the rebellion should be dismissed. In October he was appointed under secretary for Ireland, possibly in the hope that as a catholic his appointment would be welcomed by nationalists. He was popular with fellow officials, but his relations with the chief secretary Henry Duke (qv) were often strained. His description of Thomas Ashe (qv) (who had died on hunger strike) as ‘a criminal and a suicide’ (Times, 6 Nov. 1917) offended many nationalists. In March 1918 Walter Long (qv) (who had refused Lloyd George's offer to become lord lieutenant) recommended Byrne as a candidate for chief secretary, arguing that his performance as under secretary had won him respect throughout the country. Although critical of the government's timidity towards Sinn Féin in the spring of 1918, Byrne opposed the use of heavy-handed methods in dealing with public disorder and suggested a moderate and consistent approach to the problems of illegal land seizures and unauthorised military drilling. He favoured arresting those who gave seditious speeches, but did not support the readiness of the viceroy, Lord French (qv), to use the crimes act to prohibit political meetings – a policy that he believed only further alienated nationalists from the administration. He brought a memorandum to this effect before the cabinet, much to French's annoyance. After this open rupture with his superior he resigned in July 1918. Returning to his regular duties in London, he retired 24 June 1921. He lived at 3 Courtfield Gardens, London, and had a villa in Monaco. He died 11 June 1935 in London and was buried at Brompton cemetery.
He married twice: in 1910 to Maria (d. 1915), widow of William Wybrow Robertson of the ICS, and in 1919 to Alice Jane Maclennan (née Cleminson) (d. 1947), widow of Donald Maclennan of Radnor Hall, Elstree, Hertfordshire; they separated in 1928. There were no children from either marriage. A collection of his papers is held in the Colonial Office Records at the National Archives (Kew).