He was ordained in 1883 and served as a priest in the Diocese of Westminster, before returning to Rome to study, an accomplished student he gained a Doctorate of Divinity, Doctorate of Canon Law and a PhD.
He was appointed Professor at St Munchin's College, Limerick.
He was influential between the Irish Church and the Vatican and used his influence to dissuade the Vatican from condemning the 1916 Easter Rising[1] His brother Denis Riordan was a tenant farmer.
Monsignor O'Riordan died in 1919[2] His papers are held in the Irish College in Rome.
He was succeeded as Rector by John O'Hagan who had served as his Vice-Rector.