Cardinal John Henry Newman will be canonised along with a Swiss woman, an Indian nun and an Italian nun on Sunday.

An Anglican priest, he renounced an illustrious academic career at Oxford University to convert to Catholicism in 1845, convinced that the truth he sought could no longer be found in the Church of England.

Newman was held up by the Pope as a model for the faithful because he followed his conscience at great personal cost.

The canonisation of the influential Newman has been hailed by Britain's ambassador to the Holy See as an important moment in the UK's relationship with the Vatican.

Charles will lead the UK's representation at the open-air ceremony in St Peter's Square, where Pope Francis will declare the cardinal a saint in front of tens of thousands of pilgrims, the first English saint of the modern age.

Prince Charles said the cardinal had left a "lasting legacy'" as an educator, and the Catholic community owed "an incalculable debt to his tireless work".

In an article for the website of the daily newspaper of the Vatican city state, L'Osservatore Romano, Charles said the way the theologian had stood up for his "convictions" - famously shocking Victorian society by converting to Catholicism - still resonated today in light of the persecution various groups and individuals faced because of their beliefs.

Sally Axworthy, British ambassador to the Holy See, has described him as a "giant" of the 19th century, whose poetry, sermons and books went beyond a religious audience and spoke to all people.

Axworthy said it was "an important moment for the Catholic Church but also Holy See relations".

London-born Cardinal Newman, who died in England in 1890 aged 89, had been hailed by former Pope Benedict XVI as a model for ecumenism.

Australian Associated Press