Milroy, John Ignatius (‘Seán’) (1877–1946), politician and revolutionary, was born in Maryport, Cumberland, England, and came to live in Co. Cork as a young man. In Ireland he became friendly with Arthur Griffith (qv), of whom he remained a close friend and political ally, and joined Sinn Féin, serving (1909–12) as a member of its resident executive. He served three months hard labour in Mountjoy jail (June–September 1915) for an inflammatory speech delivered at Beresford Place, Dublin, and later recounted his prison experience in Memories of Mountjoy (1917). A member of the Irish Volunteers, he fought in the Easter rising and was imprisoned afterwards in England. Elected to the standing committee of Sinn Féin in 1917, he was the party's unsuccessful candidate in the Tyrone East by-election (April 1918) and also in the Tyrone North-East constituency in the 1918 general election (during which he was the party's director of elections), when he polled only 56 votes. Arrested in advance of the general election and imprisoned in Lincoln jail, he escaped with Éamon de Valera (qv) and Seán McGarry (qv) in February 1919; the escape was facilitated by a replica key smuggled into the prison, based on Milroy's drawing of a key, sent to Dublin as a 1918 Christmas card. After his escape he was involved in establishing the Irish Self-Determination League in Britain. He was never entirely comfortable with the more radical republican opinions of the new Sinn Féin.
Elected unopposed as Sinn Féin TD for Cavan in 1921, he was secretary of a committee established to advise the Irish treaty delegation on Ulster. He was also elected to the first parliament of Northern Ireland in 1921 for Fermanagh and Tyrone, but never took his seat and did not seek reelection in 1924. A supporter of the Anglo–Irish treaty, which he believed was ‘a stupendous achievement’ (Regan, 40), he was reelected for Cavan in 1922 with the help of 70 per cent of Arthur Griffith's surplus, having received only 565 first-preference votes. A series of articles he wrote for Young Ireland in 1922, that were published as The case of Ulster (1923), argued that Northern Ireland could not survive politically or economically. A member of the sub-committee that drafted the Cumann na nGaedheal constitution in 1922, he was reelected as Cumann na nGaedheal TD for Cavan in the 1923 general election, but resigned from Dáil Éireann in October 1924 as part of the ‘national group’ of Joe McGrath (qv). He based his resignation not on the government's handling of the army mutiny but on their general policy – in particular, their opposition to a protectionist economic policy, which he favoured. The only member of the national group to seek reelection in the 1925 by-elections that resulted from their resignations, he failed to gain the nomination for Cavan and stood instead as an independent in Dublin North but was defeated, having received no support from the other members of the national group. Defeated again in Cavan in the June 1927 general election, he secured election to the Irish Free State Senate in 1928 and rejoined Cumann na nGaedheal. He remained a member of the senate until its abolition in 1936, but did not seek election to the new Seanad Éireann. In 1932 he opposed the removal of the oath of allegiance. During the 1940s he worked on cataloguing the writings of his close friend and political mentor, Arthur Griffith. He lived in Dublin at 25 Fitzwilliam Sq and died 30 November 1946 in a Dublin nursing home. His papers are in the possession of Mr Conor Kenny, Galway.