Gray was from the first an orthodox evangelical, a vigorous supporter of reform in the Church of Scotland, and a pronounced enemy to all that savoured of Romish doctrine.

On 14 July 1836, he was appointed minister of the West Church (one of three parishes contained within St John's in the city centre), Perth, where he remained until 1843.

A pamphlet by him, 'The present Conflict between Civil and Ecclesiastical Courts examined,’ Edinburgh, 1839, had a wide circulation and had great influence on the schism.

In December 1841, Gray was commissioned to visit Switzerland to express the sympathy of the Free Church with the suspended ministers of the Canton de Vaud; he extended his tour to Constantinople.

[1] Robert Smith Candlish collected nineteen of Gray's sermons, with memoir and portrait, under the title 'Gospel Contrasts and Parallels,’ Edinburgh, 1862.