William Hughes Field was born at Whanganui, New Zealand, on 17 July 1861, the son of Margaret Symes Puslow and her husband, Henry Claylands Field, a surveyor, who later wrote a book on New Zealand ferns. Field received his primary schooling at Aramoho School, Whanganui. In 1874 he was awarded a scholarship to Wellington College. He attended the college as a boarder and in 1879 won a New Zealand University Junior Scholarship.
After serving his articles with C. H. Borlase, a solicitor in Wanganui, Field joined the Wellington firm of Buckley, Stafford and Fitzherbert in 1885. He was admitted a barrister of the Supreme Court of New Zealand in 1892 and a solicitor in 1893. In December 1895 he became a partner in the firm and in 1905 set up in practice with M. M. F. Luckie and George Toogood. He was to remain a partner in this firm until about 1933. Field spoke Māori and took a particular interest in laws relating to the Māori people.
On 26 April 1893 Field married Isabel Jane Hodgkins in Dunedin; they were to have three sons and two daughters. Isabel was a daughter of W. M. Hodgkins and the sister of Frances Hodgkins, and was herself a painter. On 6 January 1900 Field was elected to the House of Representatives at a by-election in the Ōtaki electorate. The seat had become vacant when his brother Henry died in office at the end of 1899. Field's entry into politics was, he wrote, 'very much against my own inclinations, for I like a quiet life'. With one three-year break he was to hold the seat for 35 years and his life was anything but quiet.
Field had been elected as a Liberal but was, in fact, more concerned with constituency than with party issues. Willie Field, as he was usually known, was extremely energetic in pressing for public works in his electorate and in supporting sectional interests such as farming and flax- and sawmilling. He also wrote innumerable letters to cabinet ministers asking them to back applications from various constituents for positions in the civil service.
Although he lived in Wellington, Field frequently visited the Kāpiti coast on electoral business or to supervise his two farms at Waikanae. He had the reputation for being a compulsive land-buyer whose practice was to buy land which he then mortgaged to buy more land. He lent money to Māori neighbours for tangihanga and other expenses, with land as security for the loan; if it was not repaid, the money owed was credited towards purchase of the land. However, he was continually short of cash and his son Peter later recalled that his mother would sometimes paint a picture 'to pay the grocer's bill'.
At the 1911 general election Field was opposed by a Socialist Party candidate, John Robertson, who had been nominated by the local flax-mill workers' union. Robertson won in the second ballot by 21 votes. In 1914 Field defeated Robertson, but not as a Liberal: he had been so upset by the waterfront strike of 1913 that he had joined the Reform Party.
Field lived in the heyday of railways and never ceased to work for a cheaper and better service on the coast; the popular 'Field's Express', which stopped at every station between Wellington and Palmerston North, was one result of his advocacy. However, when Field was promoting the service in the early 1920s he was probably also thinking of providing a convenient access to the township he was developing at Waikanae Beach. He quickly realised the importance of road transport too. From 1918 he pressed for a coastal highway to avoid the steep Paekākāriki hill, but it was not until 1939 that a coastal road was constructed – four years after Field had retired from Parliament.
The Ōtaki electorate also benefited from Field's interest in botany. He imported marram grass from Australia to stabilise the sand-dunes along the coast, making beach housing possible. He always tried to save native bush, especially in Ōtaki Gorge and other places where the bush was on land that was unfit for farming. His concern over the needless destruction of native forests led him to support measures such as the Scenery Preservation Bill in 1903 and the Public Reserves, Domains and National Parks Bill in 1928.
Field was involved with various educational bodies: he was on the Wellington College board of governors for 41 years, on the Wellington Education Board for 20 years and on the Wellington Technical College board for several years. He was captain of the Star Boating Club for a long period and rowed in representative crews. Another lifelong interest was tramping. As a young man he had walked with his father from Whanganui to the Karioi plains over the route that came to be known as Field's Track. In later years he was a member of the Tongariro National Park Board. In the Tararua Range he pioneered the southern crossing from Ōtaki over Mt Hector to Greytown, and he was a founder and first president of the Tararua Tramping Club.
William Hughes Field died in Wellington on 13 December 1944, survived by his wife and children. Walter Nash remembered him as a lovable character with the type of personality 'that lives in the hills and with Nature'. Field had seen the various possibilities of his local landscape: some of his land was farmed, or later developed for housing, but parts were carefully preserved so that the birds and bush could flourish. His chief memorials are several bush reserves around Waikanae, and Field Hut and Field Peak in the Tararua Range.