Casey is educated in Limerick and in St. Patrick’s College, Maynooth. He is ordained a priest for the Diocese of Limerick on June 17, 1951 and appointed Bishop of Kerry on July 17, 1969. He holds this position until 1976, when he is appointed Bishop of Galway and Kilmacduagh and apostolic administrator of Kilfenora. While in Galway, he is seen as a progressive. It is a significant change in a diocese that has been led for nearly forty years by the very conservative Michael Browne.
Casey is well known for his work aiding Irish emigrants in Britain. In addition, he supports the Dunnes Stores‘ staff, who are locked out from 1982 to 1986 for refusing to sell goods from apartheid South Africa.
Casey attends the funeral of the murdered Archbishop of San Salvador, Monsignor Óscar Romero. He witnesses first hand the massacre of those attending the funeral by government forces. He then becomes a vocal opponent of United States foreign policy in Central America, and, as a result, opposes the 1984 visit of United States President Ronald Reagan to Ireland, refusing to meet him when he comes to Galway.
Casey is highly influential in the Irish Catholic hierarchy, and serves as bishop until his resignation in 1992. He is a friend and colleague of another highly prominent Irish priest, Father Michael Cleary.
In 1992, newspapers discover that Casey has had a sexual relationship with Annie Murphy, an American divorcée. Together they have a son, Peter, born in 1974 in Dublin. Murphy later claims that Casey had attempted to persuade her to give the child up for adoption at birth. She chooses not to do so and raises him with the help of her parents. When Murphy decides to go public about the relationship and informs The Irish Times, Casey tenders his resignation and leaves the country.
Casey’s resignation is regarded as a pivotal moment when the Roman Catholic hierarchy begins to lose its considerable influence over the society and politics of Ireland. He is succeeded by his Secretary, Bishop James McLoughlin, who serves in the post until his own retirement on July 3, 2005.
Casey opts to embrace the life of a foreign missionary in South America. He works with members of the Missionary Society of St. James in a rural parish in Ecuador, despite his lack of knowledge of the Spanish language. During this time, he travels long distances to reach the widely scattered members of his parish. After his missionary period is completed, instead of returning to Ireland, Casey takes a position in the parish of St. Pauls, Haywards Heath, in South East England. He returns to Ireland in 2006.
In 2005, Casey is investigated in conjunction with the sexual abuse scandal in Galway, Kilmacduagh and Kilfenora diocese. He is subsequently cleared of any wrongdoing.
Casey suffers four mini strokes in 2002 and begins to experience memory issues. In August 2011, he is admitted to a nursing home in County Clare. Eamonn Casey dies on March 13, 2017 at the age of 89.