He took part in the 1980s civil rights, social justice and free speech movement in Queensland, Australia, opposed to state Premier Joh Bjelke-Petersen.
[6] O'Reilly was working as a relief teacher in Queensland when he first came into contact with the Catholic Worker Movement (CW), founded in the United States by Dorothy Day and Peter Maurin during the Great Depression.
Catholic Workers in Brisbane were also concerned about the threat posed by nuclear weapons and the uranium mining industry and its direct and indirect effects on those in the Third World.
Together with other members of the Brisbane Catholic Worker, he took an active role in highlighting the involvement and complicity of the Australian government, corporate and military sectors in supporting Indonesia's brutal and illegal 25-year occupation of East Timor.
O'Reilly publicly accused ASIO of heavy-handed tactics, saying, "I felt it was a kind of intimidation basically; they were asking what my plans were for the next three months, in terms of politically organising against Australian involvement in the war.
"[9] In a landmark case, O'Reilly went to trial at Ireland's Four Courts for the third time for disarming a US navy warplane at (civil) Shannon Airport in the early hours of 3 February 2003:[3] this group action became known as the Pitstop Ploughshares.
[4] Two earlier trials in 2005 had ended in mistrial; O'Reilly and four others (Deirdre Clancy, Nuin Dunlop, Karen Fallon and Damien Moran) were acquitted by an Irish jury on 25 July 2006.
The defence case had been that all the defendants had conscientiously believed they were acting to save lives and property in Iraq and Ireland, and that their disarmament action was reasonable, taking into consideration all the circumstances.