Gillespie was born at Kirkcaldy, where his father, John Gillespie, was parish minister. He studied at St. Andrews University as a "presbytery bursar". On graduating he became domestic chaplain to John Gordon, 1st Viscount Kenmure (d. 1634), and afterwards to John Kennedy, 6th Earl of Cassilis. His conscience did not permit him to accept the episcopal ordination, which was at that time an indispensable condition of induction to a parish in Scotland.
In April 1638, soon after the authority of the bishops had been abolished by the nation in Scotland, Gillespie was ordained minister of Wemyss (Fife) by the presbytery of Kirkcaldy. In the same year he was a member of the Glasgow Assembly, before which he preached a sermon, on November 21, against royal interference in matters ecclesiastical. It was so pronounced as to call for some remonstrance on the part of Argyll, the Lord High Commissioner.
In 1640 he accompanied the commissioners of the peace to England as one of their chaplains. In 1642 Gillespie was translated to Edinburgh; but the remainder of his life was chiefly spent in the conduct of public business in London. From 1643 onwards, he was a member of the Westminster Assembly, in which he took a prominent part: he was appointed by the Scottish Church as one of the four commissioners to the Assembly. He was the youngest member at the Assembly, but took a great part in almost all the discussions on church government, discipline, and worship. He strongly supported Presbyterianism by numerous writings, as well as by fluency and readiness in debate. One of the most notable is his well preserved encounter with John Selden on Erastianism and Presbyterian polity.
In 1645 he returned to Scotland, and is said to have drawn the Act of Assembly sanctioning the directory of public worship. On his return to London he had a hand in drafting the Westminster confession of faith, especially chapter I.
Gillespie was elected moderator of the Assembly in 1648, but the duties of that office (the court continued to sit from the 12 July to the 12 August) told on his health; he fell into consumption, and died at Kirkcaldy on December 17, 1648. In acknowledgment of his public services, a sum of 1000 Scots was voted, though destined never to be paid, to his widow and children by the committee of estates. A simple tombstone, which had been erected to his memory in Kirkcaldy parish church, was, in 1661, publicly broken at the cross by the hand of the common hangman, but was restored in 1746.
A man of notable intellectual power, he exercised an influence remarkable especially as he died in his 36th year. He was one of the most formidable controversialists of a highly controversial age. His best known work is Aaron's Rod Blossoming, a defense of the ecclesiastical claims of the high Presbyterian party.
While with the Earl of Cassillis he wrote his first work, A Dispute against the English Popish Ceremonies obtruded upon the Church of Scotland, which, published shortly after the "Jenny Geddes" incident (but without the author's name) in the summer of 1637, attracted considerable attention. Within a few months it had been found by the Privy Council to be so damaging that by their orders all available copies were called in and burnt.
His principal publications were controversial and chiefly against Erastianism:
- Three sermons against Thomas Coleman;
- A Sermon before the House of Lords (August 27), on Matt. iii. 2, Nihil Respondem and Male Audis;
- Aaron's Rod Blossoming, or the Divine Ordinance of Church-government vindicated (1646), which is regarded as an able statement of the case for an exclusive spiritual jurisdiction in the church;
- One Hundred and Eleven Propositions concerning the Ministry and Government of the Church (Edinburgh, 1647).
The following were posthumously published by his brother:
- A Treatise of Miscellany Questions (1649);
- The Ark of the New Testament (2 vols., 1661–1667);
- Notes of Debates and Proceedings of the Assembly of Divines at Westminster, from February 1644 to January 1645.
See also Works, with memoir, published by William Maxwell Hetherington (Edinburgh, 1843–1846).
- An assertion of the government of the Church of Scotland, in the points of ruling-elders, and of the authority of presbyteries and synods : with a postscript in answer to a treatise lately published against presbyteriall government .. (1641)
- An Useful Case of Conscience Discussed and Resolved: Concerning Associations and Confederacies ... (1649)
- The Works of Mr. George Gillespie (Vol. 1 of 2)
- https://archive.org/details/theworksofmrgeor26849gut gutenberg etext# 26849
- Testimony-bearing exemplified : a collection. Containing, I. Gillepsie against association with malignants; together with the causes of God's wrath, agreed upon by the General assembly of the Church of Scotland, met at Edinburgh, October 1651. II. The informatory vindication; to which is subjoined, a collection of excellent laws, (or Eschol grapes) in favours of our covenanted reformation .. (1791)
- Maclead, John. Scottish Theology in Relation to Church History Since the Reformation. Edinburgh, Scotland; The Publications committee of the Free Church of Scotland. 1943
- Francis J. Bremer, Tom Webster. Puritans and Puritanism in Europe and America: A Comprehensive Encyclopedia (2006), p. 105.
- This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). Encyclopædia Britannica (11th ed.). Cambridge University Press. Missing or empty
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- This article incorporates text from a publication now in the public domain: Cousin, John William (1910). A Short Biographical Dictionary of English Literature. London: J. M. Dent & Sons. Wikisource