William Turnbull Leach (March 1, 1805 – October 13, 1886) was a Canadian clergyman and academic.

Born in Berwick-upon-Tweed, England, the son of Robert Leach and Elizabeth Turnbull, Leach was educated in Berwick-upon-Tweed, Stirling, and received a Master of Arts degree from the University of Edinburgh.

He was licensed as a minister of the Church of Scotland and emigrated to Upper Canada in the 1830s.

In 1865 he was named domestic chaplain to the bishop and an archdeacon.

From 1846 to 1853, he started teaching at McGill College (later McGill University) as a professor of classical literature and lecturer in mathematics and natural philosophy.