O'Brien, Thomas (1914–74), poet, publisher, and Spanish civil war veteran, was born 24 April 1914 in Dublin, eldest child among two sons and two daughters of Hugh O'Brien and Mary (‘Polly’) O'Brien (née Berkeley). Having attended local Christian Brothers' schools, he left formal education aged 14. He joined the IRA as part of an influx of new members following the 1932 general election and the defeat of the Cumann na nGaedheal government. In the IRA he embraced the elements that tended more towards radical socialist politics than the military-minded wing. From 1934 he was active in the left-wing Republican Congress. In 1935 he was imprisoned in Mountjoy for one month – ostensibly to save his brother James from the same fate – for a dispute in which Congress members picketed the premises of a chain of grocery shops. By 1937 he had joined the Communist Party of Ireland and began publishing poems and articles in the left-wing publications Worker, Irish Democrat, and Workers' Republic. He also joined with such left-wing writers as Alec Digges and Seán Ó hEidirsceoil to found the New Theatre Group to produce plays in Dublin, and he himself both wrote and acted in plays. Some of his poetry from this period is included in the anthologies edited by Leslie Daiken (qv), Good-bye twilight (1936), and Devin Garrity, New Irish poets (1948).
In April 1938 he left to fight with the International Brigades for the republican side in the Spanish civil war. He travelled through London and Paris, and crossed the Pyrenees, arriving at Figueras on 14 April. He was stationed with the XV Brigade at the Catalan town of Olot. While awaiting combat he was hospitalised with a severe fever, but he recovered and saw action on 25 July as the republican forces attempted to cross the Ebro and open a corridor between the separated halves of republican Spain. Wounded, he left the front line on 1 August and was taken to hospital. He did not subsequently return to action and, after the International Brigades were stood down in mid September, he returned to Ireland on 10 December. His play ‘The last hill’, based on the war, was performed by the New Theatre Group in 1939 at the Peacock Theatre.
Both before and after his period in Spain, he endured stretches of unemployment. Through the 1940s and 1950s he wrote a number of sixpenny Wild West tales under the pseudonym ‘Harry Mancher’, including Murder on the prairie (1945). This was not the most remunerative of work and he also started a travelling library, exchanging and selling books in Dublin in the early 1940s. It became such an institution in the city that he was invited to present a programme on Radio Éireann. He lived for a time in Bray before moving to Crumlin (1951). In addition to his library, he ran tuition courses for new writers and published a crossword magazine, Second Thoughts: the thinking competitors' weekly. Along with Eleanor O'Brien (unrelated), he established a small duplicating business and then the printing company E. & T. O'Brien. In 1974 he established the O'Brien Press, publishing biographies of Erskine Childers (qv) and Peadar O'Donnell (qv), and a book of poetry by Tom Leonard. His last public act was the launch of the O'Donnell biography. He died suddenly on 6 December 1974; the graveside oration was given by a fellow International Brigade veteran, Frank Edwards (d. 1983), following a secular funeral.
O'Brien met Anne Sevitt of Portobello, Dublin, the daughter of Ukrainian Jewish immigrants, through the New Theatre Group and they married in Liverpool in 1940. She was an artist, a member of the Irish Polish Society and of the Leinster Bowling Club, and an active figure in the artistic life in Dublin for many years until her death on 3 January 1998. They had seven children, one of whom, Michael, became a central figure in the O'Brien Press.