Sir John Pentland Mahaffy (26 February 1839 – 30 April 1919) was an Irish classicist and polymathic scholar who served as the 34th Provost of Trinity College Dublin from 1914 to 1919.

Mahaffy, a man of great versatility, published numerous works across a range of subjects, some of which, especially those dealing with the 'Silver Age' of Greece, became standard authorities.

[10] Like his protégés, Wilde and Oliver Gogarty, Mahaffy was a brilliant conversationalist, coming out with such gems as "in Ireland the inevitable never happens and the unexpected constantly occurs."

He was apparently opposed to Irish Catholics accessing higher education; Gerald Griffin records Mahaffy as saying "James Joyce is a living argument in defence of my contention that it was a mistake to establish a separate university for the aborigines of this island – for the corner boys who spit into the Liffey.

In 1914, he suppressed the university's Gaelic Society when it proposed to mark the centenary of the birth of Thomas Osborne Davis with a gathering that was to be addressed by Patrick Pearse, who at the time was campaigning against the recruitment of Irish soldiers to serve in the British armed forces during World War I, whereas Mahaffy was vigorously in favour of all possible support for the British war effort.

When he moved into Earlscliffe (a house on the Hill of Howth, County Dublin) as his summer residence, a wag at the time suggested that maybe it had better be renamed Dukescliffe.

Mahaffy asked him about his studies, later lent him books to assist him, and eventually saw to it that the young man was admitted free of charge to read Classics at Trinity College Dublin.

[15] In 1865, Mahaffy married Frances Letitia MacDougall (d. 1908), by whom he had two daughters, Rachel Mary (d. 1944) and Elsie (d. 1926), and two sons, Arthur William (d. 1919) and Robert Pentland (d.