James Forbes was born Middlesbrough, Yorkshire, England on 14 July 1880. He was articled to Robert Lofthouse (1845-1901), James Alfred Lofthouse (?-1929) and Thomas Ashton Lofthouse (?-1944) of R. Lofthouse & Sons in Middlesbrough from 1897 to 1901 and remained with them as an assistant for a further year. He then worked as an assistant to John Mackenzie Knight, to A. J. Wood, and in the Architects' Department of London County Council from 1903 to 1905. He commenced independent practice in Middlesbrough in 1905, and from c.1910 to c.1914 was in partnership with John Alexander Black (1874-?) as Black & Forbes in Middlesborough.
Forbes was elected a Licentiate of the Royal Institute of British Architects (LRIBA) in 1910. Forbes had an office at 43 Albert Road, Middlesbrough in 1911. He died in Middlesbrough in 1925
Archibald Schools, Middlesbrough, 1910; Linthorpe Council Schools, Middlesbrough, 1910; Lower East Street Schools, Middlesbrough, 1910: St. Barnabas' Parochial Halls and Schools, 1910; Usher Hall, Edinburgh (1910?); drapery premises, 1910 and 1912; Love Lane School, Ponefract, 1911; "Elite" Picture House, 1921; "Scala" Super Cinema, 1921; "Marlborough" Cinema, 1921 (all at Middlesbrough). Picture House, West Hartlepool, 1921; Graythorp Garden Village, 1920-23; colliery houses at Tantoble, and at Tursdale, Co. Durham, 1921; The Crown, Middlesborough, 1923; country residences, 1904-23
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