Born in Launceston, Tasmania in 1872, he was educated at Hogg's Grammar School and Horton College, before training under the prominent church architect Alexander North. He later entered into partnership with North, gaining valuable early experience.
In 1896, Dunning moved to Cape Town, South Africa, where he worked with a firm of architects for 12 years, expanding his knowledge of colonial and commercial architecture. By 1908, he had relocated to New Zealand, establishing a practice in Timaru with local architect William Black.
Their firm, Black & Dunning, was based in the Stafford Chambers and undertook significant commissions, including the reconstruction of the Canterbury Farmers’ Co-operative Association building. One of their most distinctive contributions to the city was the Atlas Chambers, designed in an Edwardian Free Style. Its classical symmetry combined with Arts and Crafts decorative detailing made it a standout structure among Timaru's more traditional commercial buildings. The Macmillan Brown Library at the University of Canterbury holds drawings for the building.
In 1910, Dunning moved to Dunedin, entering partnership with C. Fleming McDonald. Together, they submitted entries for several major architectural competitions, including the 1911 Parliament Buildings (where they placed ninth) and the 1922 Auckland War Memorial Museum. Despite his skill and ambition, many of Dunning’s contributions were under-acknowledged during his lifetime.
His most significant work is considered to be the National Bank building on Princes Street, Dunedin (1911), although his role in its design was often misattributed. He also designed Barton’s Building in Manse Street and was involved in constructing the New Zealand Express Company Building, a project that brought him into contact with fellow Tasmanians Alfred and Sidney Luttrell.
Despite his efforts at self-promotion and clear talent, Dunning’s name often remained in the background. He did not achieve the lasting fame of some of his contemporaries, yet his buildings—especially in Timaru—continue to speak to his understated craftsmanship and eye for form.
William Henry Dunning died in Dunedin on 17 July 1933, aged 60. He was survived by his wife, daughter, and son, C. Dunning of Dunedin. His architectural legacy, though modest in scale, endures in structures like Atlas Chambers, which remain as elegant reminders of a skilled architect whose contributions deserve to be remembered.