Mac Eoin, Seán (1893–1973), soldier and politician, was born John Joseph McKeon, 30 September 1893, at Ballinlough, Granard, Co. Longford, eldest of five sons and three daughters of Andrew McKeon, blacksmith and farmer, of Molly, Aughnacliffe, Co. Longford, and Katherine McKeon (née Treacy) of Ballinlough. Ancestors of his mother had taken part in the rebellion of 1798 in nearby Ballinamuck. Educated locally at Ballinalee national school, he trained afterwards as a blacksmith with his father. When his father died (February 1913), he took over the forge and responsibility for making the family's living. In 1914 he joined the Clonbroney corps of the Irish Volunteers and was sworn into the IRB. He also joined the Gaelic League and began using the Irish version of his name about this time. Appointed OC 1st Battalion, Longford Brigade, Irish Volunteers (1919), he served a term in Sligo jail (October–December 1919), having been arrested for publicising the dáil loan. Promoted to vice-OC and director of operations for the brigade (September 1920), soon after this he became provincial centre for the IRB, with a place on the supreme council. Throughout the first half of 1920 he led arms raids on a number of RIC barracks in north Longford, and in June 1920 was coopted on to Longford county council by Sinn Féin. Mac Eoin's exploits as commander of the IRA's north Longford flying column, which carried out successful attacks on British forces at Ballinalee (November 1920) and Clonfin, near Granard (February 1921), earned him the sobriquet ‘the Blacksmith of Ballinalee’. He also achieved a reputation for chivalry for allowing medical treatment for wounded auxiliaries at Clonfin.
Mac Eoin was shot and badly wounded when he was arrested in Mullingar on 7 March 1921. Though sentenced to death by court martial in June on the charge of murdering RIC District Inspector T. J. McGrath (killed in a shoot-out in January 1921), he had in May been elected unopposed to the second dáil for Longford–Westmeath, and was eventually released (August 1921) after initial British reluctance to free him after the truce. At a sitting of the dáil (26 August) Éamon de Valera (qv) was elected president on the nomination of Mac Eoin.
During the dáil debate on the Anglo–Irish treaty Mac Eoin seconded the motion of Arthur Griffith (qv), proposing acceptance of the treaty (19 December 1921). In June 1922 he was appointed GOC Western Command in the national army, and during the civil war faced considerable opposition from the IRA in Mayo and Sligo. Though reelected for Longford–Westmeath at the general election of June 1922, he did not stand in the 1923 general election. In February 1925 he became GOC Curragh Command, a position he held until his appointment as quartermaster-general (March 1927). Having served briefly as chief of staff (February–June 1929), he resigned from the army to enter politics and was elected TD for Cumann na nGaedheal in a by-election in Leitrim–Sligo. A member of the short-lived National Defence Association in 1929–30, he was also a member of the Blueshirts during the 1930s.
From 1932 until his defeat in 1965 he served as Cumann na nGaedheal and Fine Gael TD for Longford–Westmeath (1932–7, 1948–65) and Athlone–Longford (1937–48). As candidate for president of Ireland on two occasions, he was defeated by Seán T. O'Kelly (qv) in 1945 and Éamon de Valera in 1959. He was appointed minister for justice in the first inter-party government in 1948. His ministry was controversial, marked by the influence of his strong religious views on his attitude to legislation, which led him to oppose the introduction of measures to regulate legal adoption, and the ‘mother and child’ scheme. A member of the lay catholic organisation the Knights of St Columbanus, he expressed his religious views again politically by opposing Sunday opening of public houses. He also served as minister for defence: in 1951 (March–June) and in the 1954–7 inter-party government.
He died 7 July 1973 at St Bricin's military hospital, Dublin. While in the army he lived in officers’ quarters in Athlone and the Curragh; after retiring from the army he lived at ‘St Anne's’, Garvagh, Co. Longford, and when he became a government minister purchased ‘Cloncoose’, Stillorgan Rd, Dublin. He married (21 June 1922) Alice, daughter of John Cooney and Bridget Cooney (née Meehan) of Gurteen, Killashee, Co. Longford. They had no children. Alice Cooney's nephew Patrick Cooney later served as Fine Gael TD for Longford–Westmeath (1970–77, 1981–9) and was a government minister (1973–7, 1981–2, 1982–7).
There are two portraits of Seán Mac Eoin by Seán Keating (qv) and John Francis Kelly, and a bronze bust by Desmond Broe (1921–68), all of which are in private possession. His papers are in the UCD archives. He is sometimes confused with Lt-gen. Sean McKeown (qv).