John Seddon (1725–1770) was an English Dissenter and rector of Warrington Academy.
The son of Peter Seddon, dissenting minister successively at Ormskirk and Hereford, he was born at Hereford on 8 December 1725. The Unitarian John Seddon (1719–1769), with whom he has often been confused, is said to have been a second cousin. He was entered at Kendal Academy in 1742, under Caleb Rotheram, and went on to Glasgow University, where he matriculated in 1744, and was a favourite pupil of Francis Hutcheson and William Leechman. On completing his studies he succeeded Charles Owen, D.D., as minister of Cairo Street Chapel, Warrington, Lancashire, where he was ordained on 8 December 1747. Soon after his settlement the Percival family left the established church and attached themselves to Seddon, thought to be a liberal divine of Arian views. Seddon gave private tuition to Thomas Percival.
After the closure of the private academies at Kendal (1753) and Findern, Derbyshire (1754), a project was launched in July 1754 for establishing in the north of England a dissenting academy by subscription. Seddon was one of the most active promoters of the scheme; it was due to him that the final choice fell upon Warrington rather than upon Ormskirk. On 30 June 1757 he was elected secretary, and when the academy opened at Warrington on 20 Oct. he was appointed librarian. As secretary he did not get on well with John Taylor, who had been appointed to the divinity chair; the trustees, however, sided with Seddon against Taylor. Discipline was always a difficulty at Warrington; with a view to better control, in 1767 the office of ‘rector academiæ’ was created, and bestowed upon Seddon. At the same time he succeeded Joseph Priestley in the chair of belles lettres; his manuscript lectures on the philosophy of language and on oratory, in four quarto volumes, were preserved in the library of Manchester College, Oxford.