John Grigg was baptised in the parish of Duloe, Cornwall, England, on 23 May 1828. He was the eldest of the three sons and one daughter of Christiana Nattle and her husband, John Grigg, a yeoman farmer. His mother died when he was about six or seven.
John Grigg was locally educated at a dame school and grammar school in Bodmin, where he lived with his pious, evangelical grandmother. He was then sent to a public school in Plymouth to begin training for a career in the church. John had been determined to be a farmer, but this had been considered too strenuous after a childhood accident left him partially crippled. However, his doggedness finally persuaded his father to relent.
His father died when John was about 16 or 17, and on inheriting the property, Bodbrane, he became responsible for providing for his stepmother and siblings. He had met and fallen in love with Martha Maria Vercoe; when she emigrated to New Zealand with her family, John Grigg decided to follow. After two years of negotiations he sold Bodbrane, and left for Australia on the Blackwall in 1854, arriving in New Zealand before the end of the year. He leased land at Otahuhu and began mixed farming. On 7 June 1855 he and Martha were married at Trinity Church, Otahuhu. They farmed at Otahuhu for 10 years, where, after one unsuccessful venture exporting potatoes to Australia, Grigg proved his versatility. His early achievement in establishing a pure-bred flock of Leicester sheep is indicated by his success as a show-ring exhibitor at the New Zealand Exhibition held in Dunedin in 1865. He also experimented successfully with cross-breeding Leicesters and merinos and imported much modern agricultural technology.
In late 1863 Grigg persuaded his brother-in-law, Auckland financier and businessman Thomas Russell, to join him in a partnership. They bought Longbeach, an area between the Rangitata and Ashburton rivers in Canterbury; 2,315 acres were freeholded, with another 30,000 held on lease. Much of the land was swamp, but Grigg diverted the Hinds River to drain it. By 1865 12,000 acres of Longbeach had been freeholded; the remainder was progressively purchased.
Grigg left Auckland in 1866. He bought a house for his family in Christchurch, where they stayed until 1871 when the first wooden house on the estate was enlarged to accommodate them all. Grigg initially concentrated on raising cattle for sale to the West Coast goldfields. When demand dropped, he diversified into grain production and began to stock sheep as well as Clydesdale and thoroughbred horses, and Berkshire and Yorkshire pigs. Known primarily as a stockbreeder, Grigg also made Longbeach famous for cropping thousands of acres of grain.
Longbeach saw major changes in the 1880s. John Grigg was quick to see the advantages of the frozen-meat trade. He was the founder and a long-serving director of the Canterbury Frozen Meat and Dairy Produce Export Company, and carcasses from Longbeach formed part of the first refrigerated cargo sent to London in February 1882. Partly owing to Grigg's support, Canterbury became the New Zealand leader in this trade. Stimulated by the new market Longbeach eventually increased its holding of sheep from 11,000 in 1881 to 41,000 in 1892.
There were problems, however. When the land boom of the 1870s ended, Thomas Russell insisted on selling the heavily mortgaged property. John Grigg refused, and Longbeach's stock were offered for sale in November 1882, when the self-contained village on the site helped to accommodate and feed hundreds of potential buyers from all over New Zealand. Grigg himself bought two-thirds of the stock and gradually reduced the size of the property to 15,000 acres; some of the land had already been sold, mainly to employees. Grigg survived the worst of the depression by a combination of thrift and insistence on excellence. In the same period he moved into dairy farming, importing Dutch Friesian cattle in 1883.
A dedicated nonconformist churchman in England, Grigg joined the Anglican church in New Zealand. He took an active part in local church affairs as a lay reader and a member of the General Synod. He admired Bishop George Selwyn and shared with him a sympathetic attitude toward the Maori.
John Grigg was involved in public life as well as farming. He chaired William Moorhouse's unsuccessful campaign for the superintendency of Canterbury in 1870. In the 1880s he attributed the effects of economic depression and the consequent lack of public confidence to Sir George Grey's leadership. When Sir Julius Vogel spoke at Ashburton in June 1884, Grigg was sufficiently impressed to offer himself, successfully, as a Vogelite candidate in a by-election for Wakanui in July. Too honest to act as a docile subordinate and fearful that Vogel and Premier Robert Stout would introduce a land tax, Grigg decided he was unsuited to party politics and resigned his seat in June 1885. Believing he had come to support Grey, his erstwhile constituents burned him in effigy. Grigg also served on the Ashburton Road Board from 1872 to 1879, the Ashburton County Council from 1878 to 1884 and 1887 to 1896, the local school committee, and other local bodies. He was a fellow of Christ's College and a member of the board of governors of Canterbury College from 1879 to 1894.
A man of medium stature with penetrating blue eyes and a generous beard, John Grigg has been described as active, quick-tempered, impulsive and generous. A background of generations of yeomen farmers combined with a strong faith gave him a genuine regard for the land. His forthright nature and ability to foresee and adapt to change were qualities well suited to the role of a pioneer.
When John Grigg died at Longbeach on 5 November 1901, seven of his 10 children (five daughters and two sons) survived him. He was buried beside his wife, Martha, who had died on 19 December 1884; the graves are close to the one-time Prebbleton church which John had bought and placed in the homestead grounds. Their eldest son, John Charles Nattle Grigg, who had been running the estate for several years, inherited Longbeach on his father's death.