William Saywell (1643–1701) was an English churchman and academic, known as a controversialist, archdeacon of Ely, and Master of Jesus College, Cambridge.
He was son of Gabriel Saywell (died 1688), rector of Pentridge, Dorset. After a few months passed at Cranbourne school, he went in 1659 to St John's College, Cambridge, where he was admitted a sizar. He graduated A.B. in 1663, A.M. 1667. On 2 April 1666 he was elected a fellow of his college. In 1669 he was incorporated M.A. at Oxford.
In 1679 Saywell proceeded D.D., and on 8 March in the same year was installed a prebendary of Ely Cathedral. On 9 December that year, on the promotion of Humphrey Gower to the mastership of St. John's College, he was elected his successor as master of Jesus College.
On 28 November 1672 Saywell was appointed chancellor of the diocese of Chichester, and on 22 January 1681 was collated to the archdeaconry of Ely. He gave money to Jesus College, for the adornment of the hall and the purchase of advowsons. He died in London on 9 June 1701, and was buried in the chapel of his college on the 14th.
As a controversialist, Saywell aimed at both dissenters and Catholics. His works were:
Saywell also contributed Latin verse to Hymenæus Cantabrigiensis in 1683 and to Academiæ Cantabrigiensis Affectus in 1685.