John Glas (5 October 1695 – 2 November 1773) was a Scottish clergyman who started the Glasite church movement.
He was born at Auchtermuchty, Fife, where his father was parish minister. He was educated at Kinclaven and Perth Grammar School, graduated from the University of St Andrews in 1713, and completed his education for the ministry at Edinburgh. He was licensed as a preacher by the presbytery of Dunkeld, and soon afterwards ordained by that of Dundee as minister of the parish of Tealing (1719), where his preaching soon drew a large congregation. Early in his ministry he was brought to a halt while lecturing on the Shorter Catechism by the question "How doth Christ execute the office of a king?" This led to an examination of the New Testament foundation of the Christian Church, and in 1725, in a letter to Francis Archibald, minister of Guthrie, Forfarshire, he repudiated the obligation of national covenants.
In the same year he formed a society separate from the multitude, numbering nearly a hundred, and drawn from his own and neighbouring parishes. The members of this ecclesiola in ecclesia pledged themselves to join together in the Christian profession, to follow Christ the Lord as the righteousness of his people, to walk together in brotherly love, and in the duties of it, in subjection to Glas as their overseer in the Lord, to observe the Lord's Supper once a month and to submit themselves to the Lord's law for removing offences. From the scriptural doctrine of the essentially spiritual nature of the kingdom of Christ, Glas in his public teaching drew the conclusions that: