Ó Riada's career began as a music director at Radio Éireann from 1954, after which he worked at the Abbey Theatre from 1955 to 1962.

His music still endures: his mass in Irish is still sung to this day in many churches in the Irish-speaking regions of Ireland.

After beginning school in Adare, he later attended St Finbarr's College, Farranferris and whilst he was there he received musical education from Aloys Fleischmann (Senior).

He played violin, piano and organ, and studied Greek, Latin, and Classics at University College Cork, with Aloys Fleischmann (Junior) and graduated in 1952.

As his work with Ceoltóirí Chualann developed, his engagement with the modern musical avantgarde decreased, but was never abandoned.

Ó Riada composed and directed orchestral music for theatre and film, combining traditional Irish tunes and "sean-nós" (old style) songs in the classical tradition, similar to nationalist composers such as Dvořák (Czech), Bartók (Hungarian) and Ralph Vaughan Williams (English).

In 1959 he scored a documentary film by George Morrison called Mise Éire ("I am Ireland"), about the founding of the Irish Republic.

Mise Éire brought him national acclaim and allowed him to start a series of programmes on Irish radio called Our Musical Heritage.

They recorded the soundtrack of the film Playboy of the Western World (original play by John Millington Synge) in 1962.

This featured the hymn "Ag Críost an Síol", which has become popular in its own right, and with such good phrasing, that it is (wrongly) thought by many today to be an ancient medieval tune.

Further works in the "classical" tradition include Five Epigrams from the Greek Anthology (1958) and In memoriam Aloys G. Fleischmann (1964) to words by Hölderlin.

As performed by the Chieftains, it is used as a romantic overture throughout the Stanley Kubrick movie Barry Lyndon and is the basis of The Christians' 1989 single Words.

The Irish poet Séamus Heaney included the poem "In Memoriam Seán Ó Riada" in his 1979 collection Field Work.

Two schools are named 'Scoil Uí Riada' after him: a Gaelscoil in Kilcock, County Kildare, and another, in Bishopstown, Cork City.