John Louis Petit (also known as The Reverend John Louis Petit; 31 May 1801 – 1 December 1868) was an artist and architectural historian whose paintings of buildings and landscapes, almost exclusively in watercolour, complemented his activities as one of the mid-19th century's leading writers and speakers on ecclesiastical architecture. He was a vocal opponent of the dominant architectural orthodoxies of the Gothic Revival. A huge cache of his work was held by descendants until the 1980s when it was sold, mainly in regional auctions, in large lots mixed with poorer work by his sisters.