Newton King was born at New Plymouth, New Zealand, on 21 July 1855, the son of Mary Chilman and her husband, Thomas King. Newton's parents belonged to the settlement's political and commercial élite. Mary was the sister of the local secretary of the Plymouth Company and had been a governess in London. Thomas was elected to both the House of Representatives and the Taranaki Provincial Council, serving the latter as provincial treasurer. He was involved in importing, farming and shipping, and was the inaugural local manager for the Bank of New Zealand from 1861 to 1878.
Newton was educated to the age of 16 at William Crompton's school in New Plymouth. He then became a clerk for Webster Brothers, merchants and shippers. In January 1880 he entered a partnership with Robert Bauchope, an accountant and commission agent, as auctioneer. The following year he established his own business as auctioneer, stock salesman, commission agent, and seed, produce and general merchant. King was married in New Plymouth on 13 December 1884 to St Mary St George St George.
Over the years King acquired many saleyards in Taranaki and the King Country, had a large produce auction mart in New Plymouth, and was a substantial land agent. He dealt extensively in seeds and grain, and was heavily involved in importing and exporting. Retail branches of his business were established from 1900, beginning with Stratford, followed by Kaponga, Inglewood and Hawera.
Taranaki was going ahead rapidly in the late nineteenth century and large quantities of goods and capital were required for farm development. King combined his dealing with lending, generally by providing goods on credit. He was renowned for doing so without security, simply on his assessment of the debtor's character, believing that this created loyal customers. His sole initial employee and eventual successor as chairman, Stanley Shaw, may well have served to moderate his excessive optimism.
The growth of the dairying industry in Taranaki owed much to King. During the early 1880s he shipped butter salted in kegs throughout New Zealand and to Sydney. The same product was shipped in tins to the Far East. In the latter business, and in exporting fungus to China, he worked with the Taranaki merchant Chew Chong. In 1888 King cofounded the Crown Dairy Company, which took over unsuccessful early co-operative factories at Opunake, Otakeho and Manaia. His partners in building this enterprise were James George and Richard Cock. In 1896–97 Crown was the second largest New Zealand manufacturer of dairy products, with 21 factories and skimming stations in Taranaki and southern Hawke's Bay. In 1899 the total had grown to 30, but competition from co-operatives led to its dismantling by 1910.
King promoted mechanisation in farming through agencies for agricultural implements and cream separators, and as chairman of the Ridd Milking Machine Company from 1909 to 1926. He acquired the agency for Calthorpe cars while visiting Britain in 1908, and in 1911 opened a garage. These businesses helped provide transport for his salesmen and machinery servicemen. In 1914, while in the United States, King became agent for the White and Dodge motor companies.
In 1920 King publicly floated his business as Newton King Limited, with himself as chairman and managing director. The sudden onset of the depression of 1921 led to the shares being written down from £1 to three shillings. Nevertheless, his estate was worth approximately £210,000 in 1927. Amongst other farm properties, he owned Puketiti and Nukuhakere stations on the King Country coast.
Newton King also vigorously promoted the development of the New Plymouth harbour, a difficult process, but vital to the growth of the local economy. He served on the New Plymouth Harbour Board from 1899 to his death, and was chairman from 1917 to 1922. He helped create a port suitable for 'Home' boats, and brought the first steamers direct from Britain in 1911 and 1914. In 1917 he was appointed local agent for the Shaw Savill and Albion Company, which sent seven big vessels direct to New Plymouth in that year. A large wharf completed in 1925 was named after him.
King owned several racehorses and was an official of the Taranaki Jockey Club from 1894, being its president when he died. A keen gambler, he once sparked considerable public interest in a successful bet that he could drive his buggy from New Plymouth to Urenui and back in four hours. He frequently spent evenings playing poker at the Taranaki Club.
King resided at Brooklands, a property in central New Plymouth, from 1888. He developed its gardens and opened them to the public on Sundays. His wife transferred The Gables (the old hospital) to the property in 1903. In 1933 the trustees of King's estate gave Brooklands to the town in lieu of the £7,000 he had bequeathed to public reserves.
Newton was close to his famous brother, Frederic Truby King, acting as an intermediary to their father when Truby decided to give up banking and study medicine. He named his eldest son Truby and assisted the Plunket Society financially.
Newton King died at Brooklands on 27 July 1927, survived by his wife, three sons and two daughters. Coming from a financially comfortable, but not wealthy, background, 'King of Taranaki' had utilised his great energy, business acumen and outgoing personality to develop both his own fortune and the province's economy. After 1977 the firm he founded merged with various other companies. In 1993 this larger firm restructured, the rural servicing section becoming Wrightsons Limited.