Wollongong Bishop Peter Ingham said the Catholic chapel, built in 1848, was originally supposed to be temporary, so was never dedicated.

"It began as a very simple building and then it was enlarged on a couple of occasions in its history," Bishop Ingham said.

"It didn't become a cathedral until the diocese was formed in 1952. Up until then it was part of the Archdiocese of Sydney.

"It was probably seen as a temporary church, people thinking that at one stage a new cathedral might be built."

The dedication ceremony involves special prayers and anointing the walls to set it apart as a sacred place.

Bishop Ingham said last night's Mass was more a formality because the church had already been sanctified by the religious functions it had performed over so many years.

"Think of all the generations of people who have prayed there, worshipped there, the baptisms, confirmations, reconciliations, marriages, the Masses offered there and the people who have been buried from there and the community that has been built because of it," he said.

"It's been a centre of community in Wollongong and contributes to the good of the community.

"In a secular city these churches, including St Michael's, remind us that God is part of our lives, part of our city, part of our existence."

Bishop Ingham said yesterday's date was chosen because it marked the anniversary of the death of Archbishop John Bede Polding, Australia's first bishop who commissioned St Francis Xavier's Church as the first Catholic church in the Illawarra.

The special Mass was also held to celebrate completion of an extensive $300,000 renovation of the church which included replacement of the roof and renewal of the sacristy.