Irish republican activist and writer, born in Meenmore, County Donegal. Ireland's most prominent socialist republican, he campaigned for numerous radical causes throughout his life. O'Donnell was the son of a small farmer. He fought in the Anglo-Irish War (1919–21) and became a leading figure in the Irish Civil War (1922–23), when he fought for the Irish Republican Army (IRA) against the Anglo-Irish Treaty (1921). He later joined the International Brigade in the Spanish Civil War (1936–39). His most celebrated works, which depict the harsh lives of the underprivileged, are Islanders (1927) and The Big Windows (1955).
O'Donnell began his working life as a teacher, then a trade union organizer, before becoming engaged in revolutionary politics. During the Irish Civil War (1922–23), he was captured by forces of the provisional government, but escaped after a 41-day hunger strike. A vigorous publicist and editor of An Phoblacht, the official IRA newspaper, he gave (and then withdrew) qualified support for Éamon de Valera during the election of 1932. He left the IRA in 1934 to establish Republican Congress, an unsuccessful fusion of socialism and republicanism.
O'Donnell wrote extensively on his experiences – the novel Storm (1925) had the Anglo-Irish War as its theme, The Gates Flew Open (1934) was about his imprisonment, Salud! (1937) concerned the Spanish Civil War (1936–39), and There Will Be Another Day (1963) reflected his campaign against land annuities which led to the Anglo-Irish Economic War of the 1930s. As editor of the literary monthly The Bell 1946–54, O'Donnell strongly promoted Irish writing.