He then studied law for a time but quickly changed course for a religious career and was eventually licensed by the Presbytery of Dunblane 16 August 1743.

He was ordained parish minister of Kirkintilloch, north of Glasgow, on 31 May 1744 and subsequently translated to Culross, in Fife on 21 February 1753.

Then, on 9 July 1767 he was called to Old Greyfriars Church taking up position in 1768, where he became the colleague of Principal Robertson, the historian.

His sermons were clear, vigorous expositions of a moderate Calvinism, in which metaphysical argument and practical morality are happily blended.

He was against Roman Catholic Emancipation and on the side of the American Colonies in their dispute with King George III.

(Scottish merchants had several days' advantage in crossing the Atlantic, and colonial harbours were often crowded with Glasgow ships).