Harold Thornton was born in Dewsbury, Yorkshire 14 June 1886 and studied at Liverpool University School of Architecture from 1902 to 1905. He then worked as an assistant to Henry Perkin (1847-1925) and George Bertram Bulmer (1851-1915) of Perkin & Bulmer; to Charles Reilly (1844-1928) for three years; and to William Thornton and David Thornton of W. & D. Thornton in Dewsbury.
He qualified as an architect in 1911 and commenced practice that year in Dewsbury. He was elected an Associate of the Royal Institute of British Architects (ARIBA) in 1911 and a Fellow of the Royal Institute of British Architects (FRIBA) in 1924.
His address was given as 11 Bond Street, Dewsbury in 1911 and 1914; and West Croft, Park Road, Dewsbury in 1911 and 1939.
Extensions for Dewsbury Joint Hospital, and for Slade's Royal Toffee Works; R. Thornton's warehouse and offices (4,000 yards area)