Oscar Traynor was born on 21 March 1886 in 32 Upper Abbey Street, Dublin, to Patrick Traynor, bookseller, and his wife Maria Traynor (née Clarke).[3] He was educated by at St Mary's Place, Christian Brothers school. In 1899, he was apprenticed to John Long, a famous wood carver. Traynor later qualified as a compositor.[3]
As a young man, he was a noted footballer and toured Europe as a goalkeeper with Belfast Celtic F.C. whom he played from 1910 to 1912. Traynor rejected claims soccer was a foreign sport calling it "a Celtic game, pure and simple, having its roots in the Highlands of Scotland."[2]
Traynor joined the Irish Volunteers and took part in the Easter Rising in 1916, being the leader of the Metropole Hotel garrison.[2] Following this he was interned in Wales. During the Irish War of Independence, he was brigadier of the Dublin Brigade of the Irish Republican Army and led the attack on The Custom House in 1921 and led a 12 man squad in an ambush on the West Kent Regiment at Claude Road, Drumcondra on 16 June 1921 when the Thompson submachine gun was fired for the first time in action. Three British soldiers were injured in that attack, one seriously.[4] Later Traynor was promoted to command the IRA's 1st Eastern Division.[5]
When the Irish Civil War broke out in June 1922, Traynor took the Anti-Treaty IRA side. The Dublin Brigade was split, however, with many of its members following Michael Collins in taking the pro-Treaty side. During the Battle of Dublin he was in charge of the Barry's Hotel garrison,[2] before making their escape. He organised guerrilla activity in south Dublin and County Wicklow, before being captured by Free State troops in September. He was then imprisoned for the remainder of the war.
On 11 March 1925, he was elected to Dáil Éireann in a by-election as a Sinn FéinTD for the Dublin North constituency, though he did not take his seat due to the abstentionist policy of Sinn Féin.[6] He was re-elected as one of eight members for Dublin North in the June 1927 general election but just one of six Sinn Féin TDs.[7] Once again, he did not take his seat. Traynor did not contest the second general election called that year but declared his support for Fianna Fáil.[8] He stood again in the 1932 general election and was elected as a Fianna Fáil TD for Dublin North.