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, described him as a "so-called cleric" for sharing a platform with O'Riordan. The Catholic Church stated that anyone who voted for him had committed mortal sin.