In 1731 he entered the dissenting academy run by Philip Doddridge at Northampton; to his tutor's preaching and his reading of the sermons of Joseph Boyse he attributed his religious impressions.
[2] Early in 1737 he took charge of a struggling congregation at Walthamstow, founded by Samuel Slater, a minister ejected from St. James's, Bury St Edmunds.
He at first lodged in London, only five miles away, but was then received into the family of William Snell, a chancery solicitor, and friend of Doddridge.
Farmer's preaching drew a distinguished congregation; Andrew Kippis remembered dozens of coaches in at the meeting-house door.
In 1759 his congregation relieved him of some duties by appointing as afternoon preacher Ebenezer Radcliffe, who remained his colleague till 1777.
Soon afterwards he accepted the post of afternoon preacher at Salters' Hall, vacated by the promotion of Francis Spilsbury to the pastorate; this was a presbyterian congregation, but Farmer never ceased to be an independent.
His elder brother, John, a strict Calvinist and a good scholar, became (30 December 1730) assistant to Richard Rawlin at Fetter Lane, and afterwards (28 March 1739) colleague with Edward Bentley at Coggeshall, Essex; he published a volume of sermons (1756), and succeeded Joseph Priestley at Needham Market, Suffolk (1758).
He was the champion of the divine sovereignty, both as excluding from the physical world the operation of any other invisible agents, and as authorising the production of 'new phænomena' which remove 'the inconveniences of governing by fixed and general laws.'
Farmer's positions were adopted by the rationalising section of dissenters; but in the long run his strong assertions of the fixity of natural law overcame his argument for miracles.
[2] The subject proposed the wilderness account of Christ's temptation by the Devil was a prophetic vision, rather than an actual event.