George John Hagger was born in Sutton, Surrey, England in 1878 and was articled to L. P. Rees in Redhill, Surrey from 1900 to 1903. He then went to Bourcher, Burmester & Galsworthy as an improver in 1904. The following year he commenced independent practice in Worthing, Sussex and in 1909 took over the practice of Gerald Cogswell in Worthing. In 1911 he was elected a Licentiate of the Royal Institute of British Architects (LRIBA).
Hagger's address was given as Derham House, Worthing, Sussex in 1911; 5, Highworth, Worthing in 1911 and 1914; Warwick House, Grove Road, Sutton, Surrey in 1923 and 1926; 'Argyle", Rosebery Road, Cheam, Surrey in 1930; and The Lane House, Ashtead, Surrey in 1935. He died in Surrey in 1959
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