He was a member of the Irish Volunteers and took the 1916 Easter Rising in Dublin in part. After his defeat, he was interned by the British government in Wales, United Kingdom. In the Irish War of Independence from 1919 to 1921 was Oscar Traynor commander of the Dublin Brigade of the Irish Republican Army ( IRA).
In 1925 he was elected for Sinn Féin in the Dáil Éireann, the lower house of the Irish Parliament, but took his thereat mandate in accordance with the policy of his party not true. This did not change until 1932, when Traynor was chosen for Fianna Fáil in the Dáil Éireann. From 1936 to 1939 he was Minister for Posts and Telegraphs; he served in later governments 1939-1948 and 1951-1954 as Secretary of Defense. In 1948, he became President of the Football Association of Ireland. From 1957 to 1961 he was Minister of Justice.