In later life, O'Mahony was a supporter of the Gaelic League and was president of the Maynooth Union.[1] Having "literary and antiquarian interests", he was a founder member of the Cork Historical and Archaeological Society, and contributed a number of articles to the society's journal.[1]
O'Mahony died at Crookstown, County Kildare on 4 January 1912. A statue of him, reputedly weighing 11 tons, was erected in the Catholic church in Cloghduv.[1]
^Boyce, D. George; O'Day, Alan (2021). Parnell in Perspective. ISBN9781000385656. the Cork priest John O'Mahony [..] in 1880 as a curate had incurred the wrath of his bishop by supporting Parnell's candidature
^Bolster, Evelyn (1993). A History of the Diocese of Cork: the Episcopate of William Delany, 1847–1886. Cork: Tower Books. pp. 259–275. ISBN9780902568228.
^Campbell, Fergus (2009). The Irish Establishment 1879–1914. Oxford University Press. p. 254. ISBN9780199233229. William Delany, the Bishop of Cork [..] transferred two curates (John O'Mahony and Denis McCarthy) from the city parish of St Finbarr's to the rural parishes of Kinsale and Bandon, apparently because they had supported Parnell at the Cork city election. This transfer was regarded as a demotion [..] and the two curates appealed to Rome [..] to no avail