Bryanston Square is a square in Marylebone, Westminster, London, England. Named after its owner Henry William Portman's home village of Bryanston in Dorset, it was built as part of the Portman Estate between 1810 and 1815, along with Montagu Square a little to the east and Wyndham Place to its immediate north. Its church, St Mary's, lies at the northern end of Wyndham Place and was built by Robert Smirke.
The nearest tube station is Marble Arch to the south. Montagu Square is to the east and Edgware Road is to the west. Bryanston Square is considered to be the best square in the area. with its wide roads, looked after buildings, and its magnificent garden. Wetherby Preparatory School, is situated in the south west corner of the Square
- Osmond Barnes (1834–1930), Indian Army officer, was born at No 7, Bryanston Square, on 23 December 1834. As Chief Herald of India he proclaimed Queen Victoria Empress of India at Delhi in 1877.
- Emma Elizabeth Thoyts (1860–1949, historian) was born in a house on the Square.
- Abe Bailey 1864-1940 South African politician, businessman and sportsman lived at 38 Bryanston Square. The talks which led to David Lloyd George succeeding Herbert Asquith as Prime Minister of the United Kingdom took place in Bailey's house in December 1916. Major-Gen H Lyndoch Gardiner (1820–1897) Queen's Equerry lived at No 31 Bryanston Square.
- At the south end of the square there is the William Pitt Byrne Memorial Fountain, erected in 1862, a Grade II listed monument.
- Maryna Fraser, ‘Bailey, Sir Abraham , first baronet (1864–1940)’, Oxford Dictionary of National Biography, Oxford University Press, Sept 2004; online edn, May 2006 accessed 25 Aug 2008
- "William Pitt Byrne Memorial Fountain, Paddington". British Listed Buildings Online. Retrieved 2011-03-01.