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.