John Louis Petit (1801 – 2 December 1868) was an English clergyman and architectural artist.
He was born on 31 May 1801 at Ashton-under-Lyne, Lancashire, the son of Rev John Hayes Petit and his wife Harriet Astley of Dukinfield Lodge, Lancashire, the eldest child of three boys and seven girls. He was educated at Eton College, and contributed to the Etonian. He was elected to a scholarship at Trinity College, Cambridge, in 1822, graduated B.A. in 1823 and M.A. in 1826, and on 21 June 1850 was admitted ad eundem at Oxford. He was ordained deacon in 1825, priest in 1826 and served as the stipendiary curate in the parishes of Bradfield and Mistley from 1826 until 1834<CCEd>.
Petit was one of the founders of the British Archæological Institute at Cambridge in 1844. He was also Fellow of the Society of Antiquaries, an honorary member of the Institute of British Architects, and a governor of Christ's Hospital. A learned writer and speaker on ecclesiastical architecture, he profusely illustrated his writings with drawings based on his own watercolours. Although he never tried to sell any watercolours they were highly regarded and the Architectural Exhibition Society turned over the 1869 annual meeting to a posthumous exhibition of 339 examples of his work<DNB>.
He died at Lichfield, Staffordshire, on 2 December 1868, and was buried in St. Michael's churchyard, where there was a monument with a Latin inscription to his memory.
Petit spent much time visiting and sketching churches all over Europe, starting in the early 1830s. His first publication was ‘Remarks on Church Architecture’ (1841, 2 vols.), with over 250 illustrations. This lauded the beauty of different styles of church architecture, abroad as well as in the UK, while arguing for architects to develop original work instead of copying one or other historical style. This was anaethma to the gothic revivalists, grouped around the Ecclesiologist, who advocated using only 14th Century Gothic. This debate was to continue for the rest of Petit's life and permeated all his future writing.