Hut and partook in Máirtín Ó Cadhain's Gaelic League classes as well as publishing Splannc (Irish for "Spark", named after Lenin's newspaper). O'Riordan was secretary of the 'Connolly group', composed of leftist internees, after his release from internment O'Riordan terminated his IRA membership. Political activism In 1944 he was founding secretary of the Liam Mellows Branch of the Labour Party. This branch became infamous for what was regarded during the period as its controversial nature and became an intractable enemy of Branch Chair Timothy Quill. The branch was initially established by former members of the Curragh Camp's Communist Group, including Bill Nagle and Jim Savage. During this time, the IT&GWU had disaffiliated from the Labour Party and the National Labour Party was established on the basis that communists had infiltrated the Party. Quill, who was made branch chair by the Labour Party, allegedly had O’Riordan and his fellow members expelled, with the branch being dissolved. O’Riordan later accused Quill of anti-Semitism and both Quill and T.J Murphy of “red-baiting”. In 2001, O'Riordan would claim that any attempt to raise the issue of defence of communist Spain "was shouted down at Labour Party Conferences". In 1945 he was a founding secretary of the Cork Socialist Party, whose other notable members included Derry Kelleher, Kevin Neville and Máire Keohane-Sheehan (Máire Keohane-Sheehan was the sister of O'Riordan's wife Kay Keohane-O'Riordan) Thomas Murray. O'Riordan subsequently worked as a bus conductor in Cork and was active in the Irish Transport and General Workers Union (ITGWU). He stood as a Cork Socialist Party candidate in the 1946 Cork Borough by-election, coming third behind Fianna Fáil's Patrick McGrath and Fine Gael's Michael O'Driscoll with 3,184 votes. Afterwards, he moved to Dublin where he lived in Victoria St with his wife Kay, continued to work as a bus conductor and remained active in the Irish Transport and General Workers Union. In 1948, O'Riordan was a founding secretary of the Irish Workers' League and general secretary thereafter, and of its successor organisation the Irish Workers' Party from 1962 to 1970. In the 1960s, he was a pivotal figure in the Dublin Housing Action Committee which agitated for clearances of Dublin's slums and for the building of social housing. There, he befriended Fr Austin Flannery, leading the then Finance Minister and future Taoiseach Charles Haughey to dismiss Flannery as "a gullible cleric" while the Minister for Local Government, Kevin Boland,