Plunkett, George Oliver Michael (1894–1944), republican, was born 5 July 1894 at 26 Upper Fitzwilliam Street, Dublin, fifth child and second son among three sons and four daughters of George Noble Plunkett (qv), man of letters, nationalist, and papal count, and Josephine Plunkett (née Cranny). He was educated at Belvedere College, Dublin, and Stonyhurst College, Lancashire, England, receiving officer training at the latter. His study of dentistry at UCD was curtailed by involvement in the Easter rising and subsequent incarceration. A captain in the Irish Volunteers, he commanded the so-called ‘Kimmage garrison’, formed of some seventy men enlisted into the Volunteers upon their separate returns to Ireland from Britain to escape wartime conscription, and quartered in the several months preceding the rising on the Plunkett family property at Larkfield, Kimmage, Co. Dublin. It is believed that he and Rory O'Connor (qv) set up the controversial ‘Castle document’ on a hand printing press at Larkfield. During Easter week he was attached with fifty-six men of his command to the headquarters garrison in the GPO, which included both his brothers, Joseph Mary Plunkett (qv) and John (‘Jack’) Plunkett. After evacuation of the GPO on Friday 28 April 1916, he demonstrated both humanity and courage by first rescuing a wounded British soldier stranded between lines on Moore Street, and then braving hostile fire to retrieve the man's rifle. Though he was court-martialled and sentenced to death, his sentence (like that of Jack, but not of Joseph, who suffered execution) was commuted to ten-years’ penal servitude.
Imprisoned in England until the general prisoner release of June 1917, he then worked countrywide as a Sinn Féin organiser. Appointed to the IRA general headquarters staff during the 1919–21 conflict, he travelled on inspection tours of individual units throughout the country. Serving with his brother Jack in the anti-treaty Four Courts garrison, and captured at the surrender, while imprisoned for the duration of the civil war he participated in the forty-one-day prisoners’ hunger strike (October–November 1923). Rejoining the GHQ staff upon release in 1924, he was prominent in the IRA's militarist wing, which shunned any political activity, and urged preparation for an imminent renewal of armed hostilities against the Free State government. A deeply pious Roman catholic, generally hostile to leftist tendencies in the republican movement, he nonetheless initially supported the agitation against payment of land annuities led by Peadar O'Donnell (qv). As chief scout of Na Fianna Éireann in the early 1930s, he supervised recruitment and training of substantial numbers of youths into the movement.
Plunkett was closely engaged at two pivotal moments in the tradition of legitimist republicanism. Adamantly opposed to the republican ‘new direction’ towards abandonment of abstentionism, he was instrumental in ousting Frank Aiken (qv) as chief of staff at the November 1925 general army convention, which also repealed recognition of the legitimist republican government and placed the IRA under sole control of its own independent executive. In the latter 1930s, against the entrenched opposition of the IRA leadership, he supported the plans of Seán Russell (qv) for a bombing campaign in Britain. When Russell's supporters captured control of the IRA at the April 1938 general convention, Plunkett was elected to the new army council, which adopted the bombing plan. After securing a transfer of the authority to form a republican government from the surviving legitimist members of the second dáil (who included Count Plunkett), the army council duly established itself as the de jure government of Ireland. Plunkett was among the six signatories of the proclamation of 15 January 1939 demanding withdrawal of British military and civilian personnel from all parts of Ireland at the threat of immediate war. During the course of the ensuing bombing campaign, he was arrested (August 1939) and interned in the Curragh camp.
A man of quiet determination, with a practical turn of mind bent upon increasingly impractical strategies, Plunkett cut a conspicuous figure even when incognito in his characteristic old-fashioned attire of black hat and knee breeches. He married (c.1928) Mary McCarthy; they had two daughters and three sons. After release from internment he took up farming on the property of Ballymascanlon House, Dundalk, Co. Louth, recently purchased by his parents, who also assumed residence there. He died 21 January 1944 after incurring severe head injuries when thrown from a horse-drawn cart.