[1] 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, presented by Viscountess Baltinglass, the daughter by his first marriage of Sir Peter Temple, 2nd Baronet.
[2] 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.
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.
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.
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.'
His published works include: 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.