William Mackenzie Fraser was born at Auckland on 6 April 1878, the son of Simon Fraser, a farmer, and his wife, Margaret Ann McKenzie. His father, who was attributed with finding gold at Taieri, Otago, was born in Scotland and his mother in Nova Scotia. The family lived at Point Chevalier, Auckland, until about 1890. They then settled at Maungatapere near Whangarei, where for a short time Billy Fraser attended school. He left after standard three to learn bushcraft from Maori friends and surveying from his future brother-in-law, Harcourt Buttress. For a number of years he was gum-digging, bush-felling, road-making and contract surveying in the Mangakahia district. During this time he studied by candlelight and obtained civil engineering qualifications.

From 1907 to 1918 Fraser was the Whangarei County Council engineer. In 1920 he began a 27-year association with the Whangarei Harbour Board, working as engineer, secretary, harbourmaster, treasurer and later as superintendent. At one stage it seemed he was the harbour board: as secretary he wrote to himself as engineer, then sent letters to himself in return. With energy, skill and foresight he created an efficient organisation and initiated major changes to the harbour. Under his supervision hundreds of acres of land were reclaimed from the sea. This facilitated the development of a deep-sea port, provided sites for industry and recreation and added to the income of local authorities. He also prepared the way for the establishment of fertiliser works and envisaged the construction of an oil refinery.

Fraser resigned his position as an employee of the harbour board in 1947 when he stood successfully for both the board and the Whangarei County Council at the local body elections. In 1950 and 1953 he was elected to the county council, harbour board and Whangarei Borough Council. In 1956 he stood only for the county council.

From the time he was a young surveyor in the Northland bush Fraser was interested in the native flora and fauna of the area. In the 1920s he became honorary caretaker of island sanctuaries within the Whangarei district and was a member of several expeditions to offshore islands. In 1924 he assisted a Dominion Museum expedition to the Poor Knights Islands to collect the rare lily Xeronema callistemon, which is unique to the islands. A foundation member of the New Zealand Native Bird Protection Society (which became the Forest and Bird Protection Society of New Zealand), he was vice president for over 30 years from 1927, wrote for the society's magazine and represented it on the Waipoua Forest Sanctuary Advisory Society. He was instrumental in having large areas of native bush at Whangarei Heads, Bream Head and the district's outlying islands set aside as reserves, and in having Whangarei Harbour declared a bird sanctuary in the early 1940s.

Over the years through friendship, personal gift, purchase or his own searching, Fraser accumulated about 90 Maori artefacts. Despite subsequent controversy over some acquisitions and legal problems concerning ownership, the Fraser collection, cared for by the Whangarei Museum, is a memorial to his lifetime interest in Maori lore. Fraser was himself honorary curator of the museum from 1925 until the mid 1930s. He also served on the borough library committee.

Fraser owned several properties, including a coastal dairy farm at Pataua, and he was a director of the Kamo Colliery Company and of the limeworks on Limestone Island. He was always proud of his Scottish ancestry: as well as maintaining an interest in the Old Settlers' Association, he belonged to the Waipu Caledonian and the Whangarei and County Pipe Band societies. In 1953 he created the displays of artefacts for the Waipu centennial celebrations.

William Fraser was married twice. On 31 January 1907, in Auckland, he married Caroline Featherstone Griffin, the daughter of a baronet. After her death in 1931 he married Myra Annette Vaile in Whangarei on 24 April 1937. Fraser died in Whangarei on 13 September 1960, survived by his wife, four sons of his first marriage and an adopted son and adopted daughter of his second marriage. A man of diverse interests with a 'fertile and facile mind', he is commemorated in the William Fraser Memorial Park on reclaimed land in upper Whangarei Harbour.