At age 21 he was licensed as a preacher, and receiving a call from the congregation of Burgher seceders at Selkirk, was ordained their pastor on 17 April 1771.

[2] Belying his wide reading, Lawson preached extempore with facility and simplicity.

[2] The Divinity Hall at Selkirk was an institution rather than a building, in that students lived in lodging, and lectures took place in the church and manse.

The lectures involved close reading of Bible passages in the original Hebrew and Greek.

He contributed articles to the Christian Repository, a Burgher church evangelical periodical started in London in 1815; and other papers appeared in the United Secession Magazine.

[2] Lawson is supposed to have been the original of Josiah Cargill in Walter Scott's Saint Ronan's Well.