William Duffus Hunt was born in New Zealand on 2 December 1867 at Oruru, near Mangonui, Northland, the son of John Hunt, a farmer, and his wife, Maria Frances Duffus. Hunt's father was one of the first European settlers in the Oruru valley and his mother was the daughter of the Anglican minister at Mangonui. William and his three younger sisters were educated at home by their mother and William later attended a private school in Auckland.
At the age of 18 Hunt left home and rode the length of New Zealand, finally arriving at Blackstone Hills station, Central Otago. He was employed as a rouseabout for the shearing and stayed on as a shepherd, eventually taking over the bookkeeping. By 1890 he was station manager. The station was subdivided in 1891 and Hunt organised the mustering, auction and delivery of many thousands of sheep. The Dunedin stock and station firm Wright Stephenson and Company was in charge of the sale, and the manager, J. A. Johnstone, was so impressed with Hunt's ability that he offered him a position with the firm. Hunt accepted, and was immediately sent to Gore to open Wright Stephenson's first branch office. He accomplished this despite aggressive opposition from rival agents. In 1896 he opened a branch in Invercargill and became manager for Southland.
On 20 December 1894, at Gore, Hunt married Ismene Helena Stanley, the daughter of a local Anglican minister. The couple were to have two children. Ismene Hunt died in May 1900 and on 15 May 1902 at Adelaide, South Australia, Hunt married Jessie Belstead Edwards. There was one child of the marriage.
At the turn of the century Wright Stephenson and Company was developing rapidly. In 1899 Hunt was made a partner, with 13 of the original 32 founder shares in his name. He was appointed managing director in 1906 when the firm was formed into a limited liability company, and the following year was appointed chairman, a position he retained until his death. Under Hunt's able and energetic guidance, the firm expanded into all areas of farming over the next three decades. Branches were opened throughout New Zealand as well as in London and Melbourne. Through a series of mergers and take-overs he consolidated the development of Wright Stephenson's as a major national company. Mergers were effected in 1916 with W. & G. Turnbull and Company, general merchants, and W. Gunson and Company, seed merchants, and in 1920 with Abraham and Williams, stock agents.
In 1907 the first fleet of De Dion cars was imported to replace the horses and buggies used by the firm's agents on the road (Hunt always had a great love of motor cars and motoring). Garages and showrooms were built to service the large range of cars, trucks and tractors for which Wright Stephenson's became agents. Wool stores, seed-dressing plants and fertiliser works were built in strategic locations throughout New Zealand. All branch offices had shops that sold farm requirements as well as bulk groceries and home appliances. The only commodity not handled was alcohol of any kind: Hunt was a staunch prohibitionist all his life.
In 1922 Wright Stephenson's established a stud department that specialised in pedigree stock. Before long the department was importing and exporting large numbers of pedigree animals of all breeds. In 1927 it was instrumental in founding the annual national sale of New Zealand thoroughbred yearlings at Trentham.
As the company expanded, so did Hunt's participation in public affairs. He was chairman of the Public Service Commission (1912), a member of the National Efficiency Board (1917) and of the royal commission on taxation (1924), chairman of the committee on unemployment (1930), and a member of various agricultural boards. He was also a director of several companies including the New Zealand Insurance Company and the New Zealand Branch of the Australian Mutual Provident Society. In 1932 Hunt received a knighthood for services to the agricultural industry and the business community.
The Hunt family lived in Invercargill at their home, Bainfield, until the head office of the firm was transferred to Wellington in 1918. Hunt owned two properties near Invercargill where he ran a Friesian stud and a flock of stud Romneys. He was a keen and successful exhibitor in Southland shows, a foundation member and later president of the Southland Agricultural and Pastoral Association, and a council member of the Royal Agricultural Society of New Zealand on its formation (and treasurer from 1924 until his death). For many years he was an associate of Truby King. On moving to Wellington he gave his home to the Plunket Society, and for many years it was called the Karitane–Hunt Hospital and Mothercraft Home, the Invercargill base of the society. Hunt was also chairman of the Karitane Products Society.
Hunt was a keen fly-fisherman and deer stalker. He enjoyed motor-car travel and would hold conferences with the firm's branch managers as they drove between offices. In this way he managed to personally visit every branch of Wright Stephenson's in New Zealand at least once a year. He also made regular trips to Australia and Britain, both for the firm and for the government. His last trip to London was in 1939, when he travelled by plane. During the return flight he contracted meningitis and died at Wellington on 18 September 1939. He was survived by Jessie Hunt, and his two sons.