Guard was born in London in 1791 or 1792. On 17 March 1813 at age 21, the stonecutter was convicted of stealing a quilt and sentenced to transportation and five years hard labour. At the end of his sentence, he worked as a sealer, and after five or six years had his own boat and crew.
Guard can lay credit to a number of European firsts in New Zealand's South Island. His whaling station, established at Te Awaiti on the Arapawa Island shore of Tory Channel in 1827, was the first permanent settlement in the South Island. (previous whaling stations having been seasonal) Guard's wife Elizabeth or Betty (née Parker, 1814–1870) whom he married in Sydney in 1830, was the first European woman to settle in the South Island. Guard's son, John junior (born 1 October 1831) was the first European child born in the South Island and his daughter Louisa (born late 1833) the first female child.
A year after starting the Te Awaiti station, in 1828, he started a branch whaling station at Port Underwood using the ship Waterloo. He used the ship to transport flax,whale oil and seal skins to Sydney 3 times per year, returning with supplies and trade goods. Later he had to abandon the Te Awaiti station.
In 1834 he was wrecked off the Taranaki coast in the Harriet with his wife and family and crew. The survivors were attacked by two different groups of local Maori. The wreck was plundered and 14 crew killed and 2 eaten. Betty Guard was tomahawked in the head, only her comb saving her life. Mrs Guard and her daughter were taken by the chief but the young boy of 2 1/2, was taken away from his mother and not seen for 2 months. Richard Bourke, the governor of New South Wales, dispatched HMS Alligator to Taranaki with a group of 60 British soldiers of the 50th Regiment. They landed a small party on the coast and attempted negotiations with the Maori captors to recover the eight remaining crew, Guard's wife and two children, John and Louisa, but were chased away. The Alligator was forced out to sea by bad weather. Together with the ship Isabella, it returned to the Taranaki coast and landed a detachment of sailors and marines. An arrangement was made to ransom the prisoners. The captain suspected the prisoner were being held at Te Namu Pa and landed a party there. They made contact with Maori. Guard grabbed the chief and took him back to the Alligator where he was beaten up. His wounds were then treated by the surgeon. The next day large numbers of Maori gathered on the beach but negotiations stalled until the Maori chief, Oaoiti, was brought ashore. He made a speech to the Maori captors and immediately Mrs Guard and her baby daughter were taken to the Alligator by waka but the boy was still held prisoner. While negotiations continued for his release a shot from the Pa was fired, narrowly missing a sailor. The captain ordered a bombardment of the pa that lasted 3 hours during which the Maori hostage takers raised and then lowered a white flag several times. Near the end of the bombardment a Maori held up the captive boy to indicate he had not been killed. The Alligator's surgeon landed with 100 men. The boy was handed over and the soldiers then opened fire on the Maori gathered on the beach. The Maori fled and the pa was burnt down. The surgeon was horrified at the troop's action. This was the first clash between Māori and British troops. The rescue expedition sent by Governor Bourke from Sydney was subsequently criticised by a British House of Commons report in 1835. Bourke used the kidnappings, murders and cannibalism to argue for a British warship to be permanently stationed in New Zealand.
Guard settled permanently at Port Underwood in 1836, and was still whaling off the Kaikoura coast in the 1840s. About this time onshore whaling ceased to be economically viable in New Zealand. His later life is unknown, but he probably farmed at Kakapo Bay.
- "Jack Guard and his Family", Te Papa
- Wises New Zealand Guide, 7th Edition, 1979. p. 427
- Wises New Zealand Guide, 7th Edition, 1979. p. 10.
- "New Zealand Encyclopaedia 1966: Guard Biography". Teara.govt.nz. 2009-04-22. Retrieved 2010-05-04.
- "Dictionary of New Zealand Biography: Elizabeth Guard". New Zealand Biography. Retrieved 2010-05-04.
- "New Zealand History online: The Harriet Affair 1834". New Zealand History. 2009-07-21. Retrieved 2010-05-04.
- The Voyagers. p 42-50. Paul Moon. Penguin 2014.
- Taranaki Story :The Harriet Incident. Puke Ariki
- The Harriet Affair- a Frontier of Chaos?- NZ History Net.
- Grady, D. Guards of the sea. Christchurch, 1978
- Griffin, R. H. Captain John Guard. New Plymouth, 
- Macgregor, M. Petticoat pioneers. Book 2. Wellington, 1975
- McNab, R. The old whaling days. Christchurch, 1913
- Marshall, W. B. A personal narrative of two visits to New Zealand. London, 1836