He worked relentlessly, first for the relaxation and then the complete repeal of the Penal Laws, and was a co-founder of the first Catholic Committee in 1757, along with his friend Dr. John Curry and Mr. Wyse of Waterford.

Furthermore, His mother was a niece of the only catholic allowed to practice as a barrister under the Penal laws, Terence MacDonagh of Creevagh, County Sligo, who helped his father regain a mere 800 acres at Bellanagare of the families former estates.

After initially attending a hedge school taught by the surviving Franciscans of Creevelea Abbey while also being tutored by his great uncle Rev.

[2] O'Conor was well known in Ireland from his youth, as a civil-tongued, but adamant advocate of Gaelic culture and history, who had suffered for his adherence to the Roman Catholic faith.

When James Macpherson published a spurious story in 1761 that he had found an ancient Gaelic (and Scottish) cycle of poems by a certain "Ossian", among the critics who rejected it as false was O'Conor, as an inclusion (Remarks on Mr. Mac Pherson's translation of Fingal and Temora) in the 1766 rewrite of his 1753 work.

That the issue occurred provided O'Conor the opportunity to establish Ireland as the source of Gaelic culture in the minds of the non-Irish general public.

Though the effort was promoted by many, it was largely through his effectiveness that Ireland received the recognition that it deserved as the font of Gaelic culture and the premier disseminator of literacy in ancient times.

O'Conor also strove for the presentation of Celtic Christianity as something separate from early Roman Catholicism as a means of allaying Protestant British distrust of the Catholic Irish, a perspective that has survived into modern times.

[citation needed] O'Conor's support for the first Catholic Committees from 1758 was copied nationwide, resulting in the successful, but slow, repeal of most of the Irish penal laws in 1774–1793.