President Michael D Higgins led tributes to Bishop Eamonn Casey following his death in a nursing home at the age of 89.
The controversial former Bishop of Galway and Kerry was hailed for the work he did for the Irish emigrant community in Britain and as chairman of the aid agency Trócaire.
President Michael D Higgins recognised the controversies of Bishop Casey's life which "were the source of pain to others", but said he had expressed his regret.
Bishop Casey passed away peacefully at the Carrigoran House, Retirement and Convalescent Centre in Newmarket-on-Fergus, Co Clare. He had been suffering with Alzheimer's and ill health in recent years.
President Higgins commended Bishop Casey for his humanitarian work.
He said in a statement: "I have heard with sadness of the passing of Eamonn Casey, former Bishop of Galway and Kerry.
"As chairman of Trócaire, he encouraged the organisation to become a leading NGO campaigning for justice as well as responding to humanitarian distress and poverty in the developing world.
"Other aspects of his life were the source of pain to others, for which Bishop Casey has apologised and expressed his deep regret, and he himself had the experience of pain visited on him in later life. Ar dheis Dé go raibh a anam."
Archbishop Eamon Martin praised Bishop Casey's contribution to the Church.
He said: "It is with great sadness that I learned of the death of Bishop Eamonn Casey.
"I wish to sincerely acknowledge the contribution of Bishop Casey to the work of the Irish Catholic Bishops' Conference over 23 years during his time as Bishop of Kerry and as Bishop of Galway."
Fianna Fáil leader Micheál Martin described Bishop Casey as a "passionate and energetic" Church leader.
"His work helping Irish immigrants in the UK buy homes was the foundation on which the housing charity Shelter was built, and he continued to press the case for housing with the UK government and local authorities in the 1960s," said Mr Martin.
"I want to extend my sympathies to Bishop Casey's family and friends at this time."
The chairman of Trócaire, Bishop William Crean, said Bishop Casey's work with the charity had helped millions across the world.
"Bishop Casey spoke out courageously in defence of persecuted communities overseas and was willing to place himself in danger in order to do so," said Bishop Crean.
"His campaigning, both at home and overseas, raised awareness of grave injustices and helped to bring about positive change."
That fall from grace, that evidence of human fallibility - it was the moment in time when the first crack spidered through the imposing edifice of the Catholic Church in Ireland. Nothing would ever be the same again.
A wise man once wrote that the good we do is written in sand, whereas the things that are, well, less good, are carved in stone. That's certainly true of Bishop Eamonn Casey and newspaper headlines frequently introduced him as "disgraced former bishop". And Bishop Casey certainly brought disgrace on himself, his vocational commitment and the Church he so publicly represented for decades.