John Gwynn (1713-28 February 1786) was an English architect and civil engineer of the 18th century, and one of the founder members of the Royal Academy in 1768.

Born in Shrewsbury, Shropshire, he worked initially as a carpenter, but then decided to practice as a (largely self-taught) architect and town planner, and moved to London, where he also became a friend of Samuel Johnson.

In 1749, he re-worked Sir Christopher Wren's plan for the rebuilding of London, writing An Essay on Design, Including Proposals for Exciting a Public Academy to be supported by Voluntary Subscription. Seventeen years later, in 1776, he published London and Westminster Improved, arguing that the Great Fire of London 100 years earlier had presented a golden opportunity to improve the layout of the city. He was a key figure in the introduction of the Building Act 1774 which improved standards of materials and workmanship – Bedford Square was one of the first areas of London to benefit.

In 1759, he unsuccessfully submitted a design for Blackfriars Bridge which he lost to Robert Mylne. But he retained involvement in several bridge projects. He was particularly associated with projects in Oxford, including Magdalen Bridge (1772-90), the city's workhouse (1772-1773) and the covered market (1774), and with bridges across the River Severn including one in his native Shrewsbury (the English Bridge, 1774), and others at Atcham (1776) and Worcester (1781).

He died in Shrewsbury in early 1786.