In his philosophy year there his record was: First of First in Mental Philosophy, First of First in Natural Philosophy, First of First in English, First of First in French and Solus in Italian. He was ordained in June 1895, in Waterford Cathedral and, shortly afterwards, in 1896, he took a post-graduate course in classics at Oxford University where he received an M.A. In 1898 he studied at the German universities of Griefswald and Bonn and, in the latter institution he received the degree of  Ph.D.  Some years later he received another doctorate, for Rome conferred on him an honorary D.D. He returned to Maynooth in 1900. After a brilliant concursus, he was appointed, in 1909, to the chair of ancient classics in Maynooth.

In addition to his college work, he was for many years chief examiner in Latin under the Intermediate Board, and, later, he was the chief examiner in Greek.  In 1907 he was elected to the position of Commissioner of Intermediate Education and, in 1919 he became vice-president of Maynooth College. In 1922 he was consecrated Coadjutor Archbishop of Sydney in Australia.  Owing to ill-health he resigned the Archbishopric in 1937 and returned to Ireland where he resided at Blackrock, Co. Dublin and in his bungalow at Ring, Co. Waterford.

With early and keen discernment, he saw the value of the revival of the Irish language and he flung himself into it with characteristic thoroughness. He was city-born and he did not know a word of Irish but he realised that the rich inheritance still lingered in certain nooks and corners of the country – though it was fast passing away. He spent his vacations amongst the Irish-speaking fishing-folk of Ring village (Rinn Ua gCuanach) in the west of county Waterford and he selected as his chief tutor, an aged woman who spoke the language with great fluency and with a rich ‘blas’ (accent). Fancy her honest pride when, having heard certain prophetic whisperings, she boasted to her neighbours: “Dr. Sheehan will yet be a Bishop, and I’m the mother of his Irish.” 

Soon he learned to preach in Irish and, by keeping an eye on his audience, he knew when his pronunciation was correct and his syntax in order. These, though but details, are, nevertheless, of interest inasmuch as they were the first formative influences in that Gaelic scholarship that founded the now celebrated College in Ring, and which gave to the country eight works in the Irish language that have been used as school textbooks. He was the author of A Child’s Book of Religion, of which over a quarter million copies have been sold all over the English-speaking world. He was also author of Sean Cainnt na nDéise(The Old Language of the Déise). 

One can understand that a professor of classics should excel in Irish but that a professor of classics should write a complete treatise on theology is a phenomenon of which even Erasmus never dreamed. And yet, such is the case! Volume One dealt with the Fundamentals of Religion and the Church (Apologetics) and, although ridiculously small in size for the ground covered, it left not a single problem, or objection, untouched and the same could be said for the remainder of this great work. There was in it, condensation without obscurity, classical clarity and precision, subtle inclusiveness of meaning and persuasiveness.

In 1906 he founded Ring Irish College in a small building on the Helvick Road and, in 1909, he initiated and carried through the building of the present famous residential college. 
 
Dr. Sheehan died in his home in Blackrock in March 1945. He was a gentle, retiring, saintly priest and scholar and, by his death, Waterford city lost one of its most illustrious sons; the Church a great prelate, remarkable for his pre-eminent ecclesiastical gifts and intellectual attainments, and the cause of the Irish language one of its most devoted, zealous and untiring workers.
He was buried in the little graveyard in Ring, among the people he loved.