He was the son of a solicitor, who was able to have him educated at Truro Grammar School, but, after his father's death, his mother was too poor to send him to university and so, after an apprenticeship, he practised for some time as an apothecary and physician. Guided by George Conon, the master of Truro Grammar School, Haweis was introduced to the doctrines of the evangelical revival. Sponsored by the ReverendJoseph Jane of St Mary Magdalene Parish Church in Oxford, in 1748 he entered Christ's College. There he organised a prayer group often seen as a successor to the Wesleys' "Holy Club". After graduation, he was ordained in the Church of England by the Bishop of Oxford in 1757 to serve as curate to Joseph Jane. In 1762, he was appointed to the Lock Hospital, London, under the guidance of the chaplain, Martin Madan. At this time he met Selina Hastings, Countess of Huntingdon, and preached in many of her chapels. Although offered an incumbency in Philadelphia by George Whitefield, he opted instead to become rector of All Saints Church, Aldwincle, Northamptonshire, in 1764, retaining the living until his death in 1820.
Countess of Huntingdon's connexion
In 1774 he was appointed chaplain to the Countess of Huntingdon. He insisted that no one other than a Church of England cleric be allowed to preach in any chapel where he ministered. However, once the chapels forming the Countess of Huntingdon's Connection were forced to register as dissenting chapels, Haweis withdrew from her service. By her will, the Countess of Huntingdon left management of the Connexion to four trustees. The principal trustee appointed was, most unexpectedly, Thomas Haweis, who continued to preside over the Connexion, comprising at that time about 120 chapels, even though he continued as a Church of England priest. He made every effort to ensure the Connexion kept as close to the Church of England as was possible and that only the Book of Common Prayer was used. Many of these chapels became part of the Free Church of England in 1863. Haweis was also one of the founding fathers of the Missionary Society.
Haweis' 14 sermons in "Evangelical Principles and Practice" formed part of the standard training materials for Connexion ordinands, akin to John Wesley's 44 sermons. In the early 1790s, Haweis published two books with the same title: 'Carmina Christo, or Hymns to the Saviour''.
A book of music, probably published in 1791, with seventeen hymn tunes composed by Haweis with words apparently written by Haweis.
A book of the words to hymns, published in 1792, consisting of 139 hymns, which was enlarged to 256 hymns in a second edition in 1808.
There is just one biography of Haweis. Summaries of his work are given by Bishop Frank Vaughan and by Bishop John Fenwick in their works on the Free Church of England, used in this article.