William Gilmour Wilson was born in 1856 at Rothesay. In 1872 he was articled to Robert Baldie, studying at Glasgow School of Art, and after completing his apprenticeship in 1877 he was successively assistant to Alexander Adamson and John Honeyman in Glasgow, George Fowler Jones in York, Francis Mackison in Stirling (perhaps for the Callander Hydropathic project) and William Owen of Warrington.
By 1880 he had set up independent practice at 134 Wellington Street, Glasgow, and in the same year he entered the competition for Liverpool School of Art in partnership with A.B Miller, who then moved to Wilson’s office from his previous premises at 139 St Vincent Street, their design being exhibited at the Glasgow Institute of Fine Arts the following year. They exhibited again together at the Glasgow Institute in 1882, but no more is known of Miller. Wilson had been admitted ARIBA on 3 January the previous year, his proposers being Honeyman, Jones and John Burnet, Senior. The practice appears to have initially been successful despite the severity of the recession in the early 1880s, and by c.1883 Wilson had taken James B Stewart into partnership as Wilson & Stewart.
In the early 1890s the practice appears to have run out of work; the partnership was dissolved and Stewart, who seems to have had good connections in Greenock and Port Glasgow, continued the practice on his own. It was probably at this time that Wilson moved to Warrington to work for William Owen. In the mid-1890s Wilson recommenced independent practice in Liverpool as partner of John Joseph Talbot, but by 1899 the partnership had been dissolved.
In the following year he relocated yet again in London, initially with both house and office at Bloomsbury Mansions, Hart Street, but by 1905 he had a separate house at Ardbeg, London Road, Croydon. He was admitted FRIBA on 6 March of that year, his proposers being William Flockhart, Samuel Bridgman Russell and Alfred William Stephens Cross. After the First World War the practice was relocated in central London, first at 9 Mitre Court, and then from c.1925 at 9 Warwick Court, Holborn. In 1928 he took his son John William Gilmour Wilson – who had been born in 1888 and trained in London – into partnership as W G Wilson & Son. William Gilmour and his wife Margaret (daughter of William Law of Langside), whom he had married in 1882, also had a daughter. William Gilmour Wilson was one of the founders of the Glasgow Architectural Association and was its first Vice-President. He was a Freemason, being a member of the Royal Arch Lodge no 153. He enjoyed golf, yachting and music. He retired in 1935, and died in 1943. His son continued the practice under its existing title after his retirement, until his death in 1947.