James Rounthwaite Moore Simpson [also known as J. R. Moore Simpson; as James R. M. Simpson; and as J. Moore Simpson] was born in Liverpool, England on 27 March 1898. It is not known where or with whom he trained as an architect. By the early 1920s he had moved to London where established an independent practice. He was elected an Associate of the Royal Institute of British Architects (ARIBA) in 1925. Houses designed by Simpson for the Modern Homes Exhibition at Gidea Park, Essex, in 1934 are discussed in Small Houses £500-£2500, edited by H. Myles Wright (1927 pp. 93, 108).
Simpson's address was given as 33 Northway, Hampstead, London in 1926; 4 Bedford Row, London in 1930 and 1939; and Grove House, Seymour Walk, Kensington, London in 1939. During World War Two he served as a Pilot Officer in the Roial Air Force. He died in 1966. His death was registered in Chelmsford, Essex.