Isaac Maddox (27 July 1697 – 27 September 1759) was an Anglican clergyman, successively bishop of St Asaph and of Worcester.

Isaac was the son of a Dissenter, Edward Maddox, stationer of London. He was orphaned at an early age, and brought up by an aunt who sent him to a charity school before apprenticing him to a pastry cook. However, assisted by an uncle, he resigned his apprenticeship and was tutored by Rev Hay, vicar of St Stephen Coleman Street. As a practising Dissenter, Maddox was given a grant from the Presbyterian Fund to study for the Dissenting ministry at the University of Edinburgh. Here he befriended John Horsley, who later became the father of Samuel Horsley, who at that time was also destined for the Dissenting ministry. He was awarded MA in January 1722/3.

Maddox returned to London early in 1723 and, along with John Horsley, promptly conformed to the Church of England, though he remained on friendly terms with Dissenters, notably Philip Doddridge of Northampton; and he conspicuously supported foreign Moravian Christians in the North American colonies. In 1740, foreign Protestants after a residence of seven years could become naturalized on swearing an oath of allegiance. Quakers were exempted this oath. In 1747, with Maddox's support, the exemption was extended to Moravians. In his speech in the House of Lords, Maddox insisted that

It would be beneficial "if the British nation expresses itself in favour of the [United] Brethren; for whatever benefit England confers upon this ancient confessor Church must be an encouragement to all evangelical Christians throughout the world, to expect nothing but good from this country."

On 10 March 1722/3, following his return to London from Edinburgh, Maddox was conferred Deacon by Thomas Green, bishop of Norwich, and given a curacy at St Bride's Church, Fleet Street. Soon after, on 9 June, he was ordained priest by bishop Edmund Gibson who sent him to Queens' College, Cambridge, who awarded him BA the following year. In 1724 he was given the vicarship of Whiteparish, Wiltshire, and in 1729 the rectorate of St Vedast Foster Lane, London. In the same year, he was also appointed domestic chaplain to Edward Waddington, bishop of Chichester, who gave him a prebendary at Chichester. He was awarded DD (Queens' College, Cambridge) by Royal Mandate in 1730.

The following year, 1731, Maddox married Elizabeth Price, niece of Bishop Waddington, by whom he had a son, Isaac Price Maddox, and two daughters, one of whom, Mary, married James Yorke, later Bishop of Ely.

In late 1733 he was appointed Dean of Wells.

In 1736 Maddox was elevated to the bishopric of St Asaph, though he continued to live in London, and at Westhorpe House, his country house at Little Marlow in Buckinghamshire. He only visited his diocese on occasional summers. In 1743 he was translated bishop of Worcester. He was a founder member of the Society for the Encouragement of Arts, Manufactures and Commerce in 1754. Isaac Maddox is buried in the south transept of Worcester Cathedral.