William John Polson was born at Wanganui on 6 June 1875, the elder of two children of Scottish immigrants Donald Gunn Polson, a farmer, and his wife, Janet Campbell Gillies. He grew up on his father's property, Manurewa, at Mangamahu, near Wanganui. His upbringing in a thrifty Presbyterian household contributed to his later no-nonsense approach to life and blunt directness of manner. He attended Mars Hill (Durie Hill) School, then Wanganui Collegiate School from 1885 to 1891.
After leaving school he worked on the family farm until ill health caused him to quit. While recuperating, he taught himself shorthand before taking up journalism. He worked first for the Wellington Evening Post and then for the Christchurch Press, becoming editor of its evening edition, Truth. In 1905 he founded the Political Reform League in Christchurch, which was the forerunner to W. F. Massey's Reform Party. In 1906 Polson returned to farming at Mangamahu. On 15 February 1910 at Melbourne, Australia, he married Florence Ada Mary Lamb Wilson, the daughter of a wealthy merchant. They were to have four children.
Polson served on the Wanganui County Council from 1911 to 1917 (for three years as chairman), and was a member of the Wanganui Harbour Board. However, his most notable local achievement was the Durie Hill elevator. As principal of the Matipo Land and Buildings Company, which had 58 acres at the top of Durie Hill, he planned a garden suburb with bowling and croquet greens, tennis courts, children's playground and picturesquely named streets such as The Rosary, The Shrubbery, and East and West Ways. Access from the main city up to the Durie Hill plateau was a problem. In 1916 Polson, with the support of his brother-in-law Colonel A. E. T. Wilson, began constructing an elevator. Requiring an access tunnel over 230 yards long and a shaft 65 yards high, the elevator, which carried bicycles as well as pedestrians, was a major engineering feat. It was opened in 1919 and handed over to the Wanganui City Council in 1942.
Polson became prominent in New Zealand national politics through the New Zealand Farmers' Union. He was provincial president for Wellington in 1920–21 and dominion president from 1921 to 1936. Unlike its successor, the Federated Farmers of New Zealand, the Farmers' Union was never an umbrella organisation, and in the 1920s had to compete with other farmers' organisations. One of these, the New Zealand Sheepowners' and Farmers' Federation, was critical of Polson's commitment to the Farmers' Union; since he was a substantial sheep farmer, they felt he should be loyal to their organisation. Previously, the Farmers' Union had languished under the passive leadership of Sir James Wilson, and William Massey and his ruling Reform government had taken its support for granted. Consequently, they were taken aback when, under Polson, it took an independent, even anti-government, stand on some issues, especially as Polson had been one of the initiators of the Reform Party. In 1924–26 Polson put up his own money to keep the Farmers' Union journal going, and in 1933 he set up a revived journal, Point Blank, which was published by his associate, R. L. Ferris, in Stratford. He was ably supported by his wife, Florence, who helped found the Women's Division of the New Zealand Farmers' Union and was its first president from 1925 to 1929.
William Polson first clashed with the Reform government over meat marketing. In 1919 he led a Wellington provincial Farmers' Union executive campaign to pressure the government into setting up a producers' committee. This was to travel to England to investigate difficulties and make marketing arrangements for New Zealand meat when the wartime contracts ended. Polson, who was then a director of the Feilding Farmers' Freezing Company, had researched the problems of storage space and selling meat on the open market. However, after considerable bickering between Massey and Polson, the committee was aborted without leaving New Zealand.
By 1921 the slump in product prices and fears of monopolistic marketing trusts had caused many farmers to favour compulsory, co-operative marketing arrangements. Polson pushed through a resolution at the Dominion Conference of the New Zealand Farmers' Union that year urging national marketing schemes for meat, wool and dairy produce. These were to be controlled by producers through boards with statutory powers, and they anticipated producer board legislation that was to become a significant feature of New Zealand farmers' affairs.
In 1922 Polson spearheaded a successful Farmers' Union campaign that resulted in the Meat Export Control Act. However, he considered this a rather hollow victory because the initial appointees to the New Zealand Meat Producers' Board included three members of the Sheepowners' Federation, who had strongly opposed the legislation. Subsequently, Polson bitterly lamented that the Meat Board did not use its very extensive powers to impose co-operative and orderly meat marketing. He was similarly disappointed with the failure of the Dairy Produce Export Control Board in 1926.
In 1934 William Polson promoted a Farmers' Union compensating prices scheme for dairy products, which was remarkably close to Walter Nash's guaranteed price scheme. During the Agriculture (Emergency Powers) Bill debate in Parliament he voted with the Labour opposition for an amendment to guarantee prices to farmers. However, in 1936 he opposed Nash's Primary Products Marketing Act because it transferred control from the producers to the bureaucrats. Polson's consistent advocacy of producer control was evidenced in the passage of the 1939 Meat Act, when he successfully moved the 'open door' amendment. This required licensed meat operators to process stock for farmers who wished to market on their own account.
Rural finance was a major concern to William Polson, who had business experience with numerous directorships, including the chairmanship of (FAME) Mutual Insurance Guaranteed Incomes Limited. His knowledge of farmers' problems on marginal land convinced him that the collapse of the ill-conceived post-war farm settlement scheme was more a result of insufficient development capital than the produce price slump of 1920–21. A Farmers' Union campaign led to a Rural Credit Associations Act being passed in 1922, but in 1923 Polson declared that the act was like the work of 'an enemy of the primary producers'.
Polson's continuous agitation for improved rural finance, including the establishment of an agricultural bank, embarrassed the Reform government into setting up a Royal Commission on Rural Credits in 1925. This travelled to Europe and North and South America and returned to New Zealand in 1926. Polson was a member and his wife, Florence, who was proficient in languages, travelled with them and assisted with translating. However, the consequent legislation, the Rural Advances Act 1926 and the Rural Intermediate Credit Act 1927, did not go far enough to satisfy Polson. He regarded the finance minister, William Downie Stewart, as a protagonist of urban business interests, and the prime minister, Gordon Coates, as the typical devious politician, whom he never trusted subsequently.
In 1928 William Polson stood successfully as an independent candidate for the Stratford electorate. He had declined the United Party nomination, believing that a non-partisan stance befitted the leader of the Farmers' Union. Throughout the 1920s he had difficulty maintaining the neutrality of the union, especially as the Auckland provincial Farmers' Union pushed to form a Country Party. He opposed town-versus-country cleavages and political policies that he considered to be socially divisive, like those of the Labour and the Country parties. His attempts to keep the Farmers' Union unified by mediating with Country Party advocates earned him the abuse of Reform stalwarts within the union. In the event, the Auckland union broke away from the New Zealand Farmers' Union, becoming a separate organisation after 1928.
In 1936 Polson resigned as Farmers' Union president, largely because many branches considered his strong anti-Labour sentiment and association with the embryonic New Zealand National Party to be incompatible with the Farmers' Union motto, 'Principles not Party'. In 1940 he played a key role in the National Party leadership struggle in which the Gordon Coates–Adam Hamilton faction was defeated by S. G. Holland. In a bid to preserve unity between National's rural and urban sectors, Holland retained Polson as a close confidant and unofficial deputy leader of the opposition. In 1942 Polson became minister of primary production for war purposes in the short-lived War Administration, and in 1943 he was acting leader of the opposition. During this period he strongly advocated deployment of New Zealand forces close to home, rather than in Europe.
Florence Polson died on 14 May 1941 and on 1 July 1943 at Christchurch William Polson married Mary Victoria Cracroft Grigg, the National MP for Mid-Canterbury and widow of A. N. Grigg, the previous MP for that electorate. Polson retired from Parliament in 1946, when his Stratford seat was eliminated by electoral boundary changes, and in 1948 he returned to the family farm, Manurewa. In 1950 Holland, now prime minister, appointed Polson leader of the last Legislative Council, which acquired the epithet 'suicide squad'. His job was to disband the Council and he earned Holland's lasting gratitude for his delicate handling of a difficult issue.
His interest in farm politics never waned. He was made a life member of the Federated Farmers of New Zealand at its inception in 1946 and attended and addressed meetings regularly until his 85th year. In 1951 he was appointed KCMG for his services to farming. It could be said that Polson began by campaigning against the political establishment but eventually become absorbed by it. None the less, he was remarkably successful in sustaining for a long period a forceful, independent representation of the disparate and divisive New Zealand farm sector. He died at his home, Manurewa, on 8 October 1960, survived by his wife, Mary, and two sons and a daughter from his first marriage.