He completed his theology studies at the Pontifical Irish College, and was ordained to the priesthood by Archbishop Luigi Traglia on 21 February 1959 in the Archbasilica of Saint John Lateran.
On his return to Ireland, he was appointed to the staff of Coláiste Éinde, Salthill, while studying for a higher diploma in education at University College, Galway.
Following the sudden death of Michael Harty on 8 August 1994, Walsh succeeded to the see, and was ordained as Bishop of Killaloe by the Archbishop of Cashel-Emly, Dermot Clifford, on 2 October in the Cathedral of Saints Peter and Paul, Ennis.
[1] As part of Jubilee 2000, Walsh began a three-week Pilgrimage of Reconciliation, as a way of "recognising, acknowledging, painful though it may be, serious wrongs have been done, and deep hurts have been caused by people working with our church down the years".
[7][8] In an interview with The Irish Times in November 2010, Walsh expressed personal views on key issues such as homosexuality, birth control and family planning, the ordination of women, clerical celibacy and the existence of the afterlife.
He asserted to have been "stunned" upon hearing about the publication of Humanae vitae, a document reaffirming traditional church teaching on family planning, in 1968, saying that "[that] was a watershed.
Connell released "a personal statement" on 26 November, noting that it had been "severely critical of the diocesan response (to abuse allegations), particularly in [his] earlier years in office", expressing his "distress and bewilderment" that priests could behave in such a way.
He also wished "to express without reservation [his] bitter regret that failures on [his] part contributed to the suffering of victims in any form", apologising to those hurt and asking forgiveness.
Tom Ryan told Walsh, "we love you", and thanked him for his fifteen years of inspirational leadership on both a diocesan and a national level.
In accordance with canon law, Walsh submitted his episcopal resignation to the Congregation for Bishops on his 75th birthday on 16 January 2010, but was expected to remain in the see until a successor was appointed.
[21][22] At a civic reception held in Ennis honouring his service on 26 March 2010, Walsh received a standing ovation and said that the position of Irish bishops was hazardous for sad reasons, and at risk from mistakes made up to 50 years previously.