Sir John Barnard (c. 1685 – 28 August 1764) was a British Whig politician and Lord Mayor of London.
Barnard was the son of a Quaker merchant from Reading, Berkshire, also named John Barnard and his wife, Sarah, daughter of Robert Payne of Play Hatch in Oxfordshire part of Sonning. He abandoned the Quakers early in his life, and is said to have been baptised into the Anglican faith by Henry Compton, Bishop of London.
The younger John Barnard initially worked alongside his father as a London City merchant. He was elected at the 1722 general election as one of the four Members of Parliament (MPs) for the City of London.
Barnard was a vigorous campaigner for the commercial interests that were his principal City of London constituency. In 1734 he successfully promoted an Act of Parliament "to prevent the infamous practice of ". This Act, which was renewed in 1737, later became known as "Sir John Barnard's Act" in recognition of his efforts. In 1736 he augmented his position as a Member of Parliament with selection as a Sheriff of London.
His campaign for City interests continued in the Parliament of 1737, with proposed legislation to reduce interest payments on the national debt, thereby lowering commercial taxation. A further clause would have introduced a Playhouse Act to regulate operation of theatres in the City of London, the disorderly operation of which posed risks of local theft or property damage. Both measures were defeated by the Parliamentary majority headed by Sir Robert Walpole. Nonetheless, Barnard's advocacy was rewarded via election as Lord Mayor of London later in the year.