In the early years of his ministry he was a leader in the Cambuslang and Kilsyth Revivals, and became a trusted correspondent of George Whitfield and Jonathan Edwards.
Taking his stand, with the majority of the Presbytery, against the Inverkeithing Intrusion, he was summarily deposed by the General Assembly of 1752.
In 1761, with two other ministers and their flocks, he formed a new body — the Presbytery of Relief, which had attained a quite considerable place in many parts of Scotland, by the time of his death in 1774.
In 1738 he went north to attend the seminary run at Perth by William Wilson (1690–1741) of the Secession Church; but was not impressed and moved on after a short while.
[4] The presbytery of Dunfermline agreed to sustain as valid the ordination he had received in England, and to allow a qualification of his subscription to the church's doctrinal symbol, so far as it had reference to the sphere of the civil magistrate in matters of religion.
[11] Gillespie absented himself from presbytery meetings held to ordain Andrew Richardson, an unacceptable presentee, as minister of Inverkeithing, in southern Fife not far from Carnock.
He was then deposed by the General Assembly of the Church of Scotland of 1752. for maintaining that the refusal of the local presbytery to act in this case was justified.
[6] The context was the rise of the Moderate Party of the Church of Scotland, from 1751, led by William Robertson with a group of younger ministers including Hugh Blair, Alexander Carlyle and John Home.
[13][14] John Witherspoon wrote the anonymous Ecclesiastical Characteristics (1753) to satirise the Moderates, and James Baine became a supporter of Gillespie.
The Marquess was on good terms with Selina, Countess of Huntingdon, and supported George Whitefield; his objection to the evangelical Boston was personal, rather than theological.
Gillespie became involved, first suggesting Thomas Scott of Hexham as minister for the seceders, who was in poor health and declined.
[20] Early expansions of the Presbytery were after secessions at Blairlogie (where William Cruden was rejected by the General Synod in 1760, and Auchtermuchty where Thomas Scott of Hexham came as minister in 1763.
[6] Gillespie's only literary works were an Essay on the Continuation of Immediate Revelations in the Church, and a Practical Treatise on Temptation.