As the archdiocese is the metropolitan see of the ecclesiastical province that encompasses Southern Ontario and part of Northwestern Ontario in Canada, the archbishop also administers the bishops who head the suffragan dioceses of Hamilton, London, Saint Catharines, and Thunder Bay.

[3][4] On March 18, 1870,[A] the diocese was elevated to the status of archdiocese by Pope Pius IX while the First Vatican Council was in session.

John Joseph Lynch became the first archbishop of the newly-formed metropolitan see,[3][6][7] and received the pallium during his sojourn in Rome to attend the council.

Five archbishops – James McGuigan, Gerald Emmett Carter, Aloysius Ambrozic, Thomas Collins, and Leo – were elevated to the College of Cardinals.

[8] Power, the first ordinary of the archdiocese, was also the first English-speaking bishop to be born in Canada.