William Terrence McGrattan (born 19 September 1956) is the eighth and current bishop of the Diocese of Calgary.

After ordination, Father McGrattan served three years as associate pastor at St. Joseph's Parish in Chatham, Ontario.

He became a member of the faculty at St. Peter's Seminary in London, Ontario, where he served as dean of theology, becoming rector in 1997.

[3] McGrattan was ordained Titular Bishop of Furnos Minor on 12 January 2010 at St. Peter's Cathedral Basilica in London, Ontario.

[4] He was appointed Bishop of Calgary, Alberta, Canada on 4 January 2017 but continued to serve as Apostolic Administrator until his successor was installed.