James Diggle Mould was born in Glossop, Derbyshire, England in 1856 and was articled to Charles John Maycock (1838-?) and Asahel Pilkington Bell (1846-1891) of Maycock & Bell in Manchester from 1872 to 1877. He then remained with Maycock as an improver and assistant for a year. During his time with Maycock & Bell, he was a Manchester Society of Architects' Students Prizeman in 1875 and 1876. From 1878 to 1883 Mould worked as head assistant to Thomas Haselden (1945?-1888) in Bolton, Lancashire.
Mould commenced practice as an independent architect in Manchester in 1883. He passed his professional exam in 1888 and was elected an Associate of the Royal Institute of British Architects (ARIBA) later that year. In 1898 he formed a partnership with his brother Samuel Joseph Mould (1870-1923), J.D. & S.J. Mould, which had an office at 58 Queen Victoria Street, London and in Bury, Lancashire. In 1900 they were joined by Austin Porritt (1875-1939) and the practice was renamed Moulds & Porritt. The partnership was dissolved in 1907.
James Diggle Mould was elected a Fellow of the Royal Institute of British Architects (FRIBA) in 1907. He was also a Fellow of the Manchester Society of Architects and Secretary of the Manchester Architectural Association from 1885 to 1891. He died in Bury, Lancashire on 28 May 1935
Hotel Majestic, St. Anne, *Ilford, 1903, and *Newlands, Hull, 1905; and over 60 other churches and chapels. Union Banks: — *Bury, 1905; *Rochdale, 1906; Nelson, 1911; and at Heywood, 1908. Silver Street Chambers, Burr, 1894; Victoria Buildings, Bury, 1897; 40 workmen's houses, Howwood (Renfrewshire), 1913-14; 20 cottages (instalment of complete scheme), Unsworth (Bury), 1921-22. (All except the two last-named in conjunction with his brother, S. J. Mould, as partner; those marked * in conjunction with Austin Porritt, as partner 1900-7)
Directory of British Architects 1834-1914. Compiled by Antonia Brodie, et al. Volume 2: L-Z. London; New York: British Architectural Library, Royal Institute of British Architects/Continuum, 2001