Born and raised in Guelph, Ontario, Thomas Collins was ordained a priest in 1973.  He considered other paths, but was inspired by a high school English teacher who suggested he should consider the priesthood.

He earned undergraduate and master’s degrees in English, later pursuing theological training in Rome.  Specializing in the Book of Revelation, he earned his licentiate in sacred scripture from the Pontifical Biblical Institute and a doctorate in theology from the Gregorian University.

He was named Bishop of St. Paul, Alberta in 1997 and Archbishop of Edmonton in 1999.  Pope Benedict XVI appointed Archbishop Collins as Archbishop of Toronto in December 2006.  On February 18, 2012, he was elevated to the College of Cardinals in Rome.  Cardinal Collins was one of 115 cardinal-electors to participate in the 2013 Conclave in Rome, where Pope Francis was elected to succeed Pope Benedict XVI.

On March 25, 2023, Cardinal Collins became Archbishop Emeritus of the Archdiocese of Toronto.