He belonged to a clerical family living in the neighbourhood of Kettering and Wellingborough, Northamptonshire. He was educated first at Strixton in Northamptonshire, and was admitted a sizar of Clare Hall, Cambridge, on 16 May 1661, graduated B.A. in 1664, and M.A. in 1668. After acting as curate at Isham in Northamptonshire, he was presented on 21 October 1668 to become vicar of the village of Stantonbury in Buckinghamshire (then virtually deserted, having no vicarage, and he may really have been chaplain to Sir John Wittewronge); he left for the rectory of Water Stratford in the same county on 28 January 1674, by the widow of Sir Peter Temple.
Under the influence of James Wrexham, a puritan preacher at Haversham, formerly vicar of Kimble Magna and of Woburn, Mason's thoughts turned to the prospect of the millennium, and he constantly suffered from pains in the head. He was sensitive to noise, and retired to an empty house, where even the sound of his own footsteps and his low voice when he prayed caused him pain. He was liable to vivid and terrifying dreams, and subject to visual hallucination. His wife died in February 1687; in 1690 he preached a sermon on the parable of the ten virgins, an attempt to interpret apocalyptic passages of scripture in the light of recent events. The sermon, repeated in other places, made some stir, and was published in the following year. About the same time he ceased to administer the sacrament in his church, and preached on no other subject than that of the personal reign of Christ on earth, which he announced as about to begin in Water Stratford. His teaching attracted some believers , to whom he expounded an extreme form of predestination doctrine. An encampment of his followers was formed on the plot of ground south of the village, called the 'Holy Ground,' where a rough life in common was carried out. Noisy meetings took place in barns and cottages, and dancing and singing was kept up day and night in the parsonage. He described to a crowd from a window in his house on Sunday, 22 April 1694, a vision of the Saviour, which he had experienced, he said, on Easter Monday, 16 April. From that time he used no more prayers, with the exception of the last clause of the Lord's Prayer, but announced that his work was accomplished, as the reign on earth had already begun. He died of a quinsy in the following month, and was buried in the church of Water Stratford on 22 May 1694. The belief in the coming millennium, and in the immortality of their prophet, was firmly rooted in the minds of his followers; and some refused to credit his death. The succeeding rector, Isaac Rushworth, had the body exhumed, and exhibited to the crowd, but many remained unconvinced, and had finally to be ejected from the 'Holy Ground.' Meetings in a house in the village continued for sixteen years afterwards.
The parish register of Water Stratford records the baptisms of four sons and one daughter of John Mason and Mary his wife between 1677 and 1684. John (born 1677) became a dissenting minister at Daventry, Northamptonshire, at Dunmow, Essex, and at Spaldwick, Huntingdonshire, successively. He died at Spaldwick in 1723, and was father of John Mason (1706—1763). William (born October 1681) was B.A. of King's College, Cambridge, in 1704, instituted to the vicarage of Mentmore-with-Ledburne, Buckinghamshire, on 23 December 1706, and was also rector of Bonsall, Derbyshire, from 1736 to 1739. He died on 29 March 1744, and was buried at Mentmore. An elder daughter, Martha, was born at Stantonbury.
