William Nicholson (1 November, 1591 – 5 February, 1672) was an English clergyman, a member of the Westminster Assembly and Bishop of Gloucester.
The son of Christopher Nicholson, a rich clothier, he was born at Stratford St. Mary, Suffolk, on 1 November 1591. He became a chorister of Magdalen College, Oxford, in 1598, and received his education in the grammar school attached to the college. He graduated B.A. in 1611, and M.A. 1615. He was a bible clerk of the college from 1612 to 1615. In 1614 he was appointed to the college living of New Shoreham, Sussex. He held the office of chaplain at Magdalen from 1616 to 1618. He was also chaplain to Henry Percy, 9th Earl of Northumberland, during his imprisonment in the Tower of London, from 1606 to 1621, and was tutor to his son, Lord Percy.
In 1616 he was appointed master of the free school at Croydon. He held the post till 1629, when he went to Wales, having been presented to the rectory of Llandilo-Vawr, in Carmarthenshire, in 1626. In 1644 he was made archdeacon of Brecon. The year before he had been nominated a member of the Westminster Assembly of divines, probably through the interest of the Earl of Northumberland, but he speedily withdrew, together with the most of the rest of the episcopalian clergy. When deprived of his preferments by the parliament he maintained himself by keeping a private school, which he carried on in partnership with Jeremy Taylor and William Wyatt at Newton Hall ('Collegium Newtoniense'), in the parish of Llanfihangel Aberbythych, in Carmarthenshire. One of his pupils was Judge John Powell. With Taylor, he wrote in the defence of the doctrine and discipline of the church of England, and in illustration of her teaching. His Exposition of the Apostles' Creed and Exposition of the Church Catechism were both written for the instruction of his former parishioners at Llandilo.