William George Horseman was born in Islington, London, England on 24 February 1869. He was articled to William Burrough Hill (1845-1941) in Southampton, Hampshire from 1886 to 1890 and remained with him as his assistant until 1891. He then worked as an assistant to Frederick Moore Simpson (1855-1928) in 1891-92, and to Edward Prioleau Warren (1856-1937) from 1892 to 1898 when he set up his own independent architectural practice in London. He was elected a Licentiate of the Royal Institute of British Architects (LRIBA) in 1911. His address was given as 27, Sackville Street, Piccadilly, London in 1906 and 1914; 57, Addison Road, Kensington, London in 1911 and 1914; 5 and John Street, Bedford Row, London in 1923 and 1926. He died in Southampton, Hampshire in 1933
Church of St. Barnabas. Epsom (1908-09) in conjunction with Albert Charles Williams (1869-?); enlargement of Church of St. Barnabas. Epsom (11924-25); estate buildings, North Mymms Park. Herts; "Abbeyfield", Guildford; Church of St. James, Barton Hartahorne, Bucks; estate buildings, Barton Hartshorne; No. 14, Berkeley Square; steam yacht "Joyeuse"; Nast Hyde, Herts; Parish Hall, Wick, Sussex.
Directory of British Architects 1834-1914. Compiled by Antonia Brodie, et al. Volume 1: A-K. London; New York: British Architectural Library, Royal Institute of British Architects/Continuum, 2001