Born at Chowbent, of Unitarian stock, he became an itinerant in 1752, but resigned in 1765, referring slightingly to the Church as 'Old Peg'. He settled at Little Leigh and became the leader of the Methodist society there; then returned to the itinerancy in 1776, but finally withdrew in 1784 because Wesley did not include him in the Legal Hundred. He became an Independent minister at Southborough, Kent. When he became ill, he received help from the Preachers' Fund and Wesley found him a teaching post.
His son John Hampson junr (1753-1819; e.m. 1777) was educated at Kingswood School and St Edmund Hall, Oxford. He was stationed in Ireland and northern England, but left the itinerancy with his father in 1784, partly because of a disagreement with Samuel Bradburn and partly because of an offer by some Sunderland laymen to fund him through Oxford, where he graduated BA in 1791 and MA in 1792.. He was ordained and became a curate, and later rector, in Sunderland, 1795-1819. His three-volume biography of John Wesley (1791) was the first to appear after Wesley's death; it was too candid to be acceptable by contemporary Methodists, but its value has become increasingly recognized. His preaching was represented by his Sermons on Several Subjects from the Old Testament (1809).
'Hampson tried to draw a picture of Wesley that was "not flatteringly disgusting, nor exaggerated to deformity, but as nearly as possible, a just transcript of truth and nature". He admits in the preface to an interest in the "foibles" as well as the "excellencies" of the man… Hampson marshaled his sources to support his contention that Wesley's judgment was not always sound. He also criticized some of Wesley's doctrines. He felt that where Wesley's opinions were scriptural and just, they did not differ from the doctrines of other denominations; where the opinions were peculiar to Wesley himself, they were either "not true, or dubious, or indifferent". And, as might be expected, Wesley's establishment of the Deed of Declaration also came under especially intense criticism in this biography… Although many later critics also saw Hampson's work as less than friendly, some have nevertheless acknowledged that his description of Wesley's character and appearance is one of the best firsthand accounts. It is often quoted by biographers in later generations.'
Richard P. Heitzenrater, The Elusive Mr. Wesley (Nashville, 1984) II pp.169-70