John Keir was born on February 2, 1780, in Bucklyvie, parish of Kippen, Scotland.

He was a Presbyterian clergyman and educator. In 1799, he entered the University of Glasgow but did not graduate. He taught school during training in divinity at the theological hall of the General Associate Synod in Whitburn (1803-1806). About 1807 he was licensed by the Presbytery of Glasgow and in 1808, attracted to the colonial missions, he sailed to Nova Scotia to serve at the Secession congregation in Halifax. In 1810, he was assigned to Prince Edward Island where he was ordained at the Princetown (Malpeque) congregation. He was also active in the promotion of education, especially a mission to encourage sabbath schools on the Island. By 1827 the Prince Town Female Society, established in 1825 in Keir’s congregation with his wife as a treasurer, was purchasing books for such schools. In 1822, he presided over the creation of a school at Princetown and became its rector. The school was recognized as the district grammar school in 1825. He also established a library for his parishioners. In the 1850s, he was president of the first Literary and Scientific Society on the Island and a member of the provincial board of health. In 1843, Keir was named Principal Professor of Theology at the Presbyterian Divinity College for the Lower Provinces. In 1852, he received an honorary degree of D.D. from Amherst College, Massachusetts. He was the author of the book "Course of Study in Systematic and Pastoral Theology and Ecclesiastical History, for Students Attending the Theological Seminary of the Presbyterian Church of Nova Scotia" (1857). His house in Malpeque, Prince Edward Island, is registered as a Canadian Landmark and is known today as Keir House.

In 1808, he married Mary Burnett. He died on September 23, 1858, in Truro, Colchester County, Nova Scotia.