The Diocese of St. Catharines underwent considerable change and consolidation from 1982 to 1997, in terms of episcopal leadership, spiritual renewal, the first ever lay diocesan congress, and Catholic secondary schools.

Bishop John A. O'Mara made the congress the primary diocesan instrument to prepare local Catholics for the Great Jubilee in the year 2000.

Priests and people have also celebrated many notable anniversaries and undertaken a number of church renovations and expansions, the most impressive among them being the wholesale restoration of the cathedral.

He had been bishop for twenty years, from 1958 to 1978, during which time he guided the local church through the many reforms in liturgy and governance brought about by the implementation of Vatican II.

Major renovations and expansion have been carried out at Lakeshore Catholic, St. Paul, Notre Dame, Denis Morris and Holy Cross.

There was much sickness in the work camps and Dr. Constantine Lee, then Pastor at St. Catharines, contracted one of the diseases while ministering to the workers and died in the winter of 1842–43.

It symbolizes the desire of the Diocese for peace with its neighbours in the United States of America, as well as within the local Niagara Peninsula community, an area of Canada which has had more than its share of battles over the centuries.

There were twenty religious communities of fathers, brothers, and sisters who ran a wide variety of educational, social, medical and charitable institutions within the Diocese.