John Whitney was born on 27 June 1836 at Shrewsbury, Shropshire, England, the son of James Whitney, a chemist, and his wife, Sophia Caroline Carline. After attending school at Shrewsbury, he obtained a commission in 1858 in the British Army, serving mainly in Ireland. On 18 April 1860 John Whitney married Harriet Sarah Chaworth Musters at Colwick, Nottinghamshire. They were to have three sons and three daughters. On the death of his father John inherited the Whitney estates of Calver Hill in Herefordshire, which he sold. In 1884 he and his family emigrated to New Zealand, arriving in Auckland on the Waihora at the end of the year.
Soon after Whitney's arrival in New Zealand the Pendjeh crisis – the Russian occupation of northern Afghanistan – caused a major war scare which affected the whole of the British Empire. He immediately volunteered to serve in the colonial forces. Whitney was given the rank of captain and command of the battery in 1885 at Point Resolution, Auckland, and was appointed assistant aide-de-camp to the commander of the colonial forces, Major General Sir George Whitmore.
This crisis highlighted the lack of an imperial ammunition reserve. Britain, forced to retain all munitions manufactured, ceased to export small arms ammunition to New Zealand. With supply suspended and stock low, the minister of defence, John Ballance, urgently sought a New Zealand manufacturer. Recognising the opportunity and utilising his military experience, in 1885 Whitney formed a partnership to produce munitions with W. H. Hazard, a gunsmith from Auckland. However, their lack of experience led to a dismal initial attempt to manufacture cartridges. Hazard quit the partnership, leaving Whitney heavily in debt. That same year Whitney established a private company, Whitney and Sons, to manufacture ammunition in New Zealand. His first task was to arrange for the local production of all the tools, appliances and machinery necessary for ammunition manufacture. He then recruited 25 workers, mostly children, and commenced production. After the introduction of the Factories Act 1891, which banned children from working in factories, he employed mainly women.
The first delivery of about 5,000 Snider ball cartridges was made to the government within 12 months. Despite the large number of complaints about the unreliability of the cartridges, demand became so great that by the end of 1887 about two million rounds had been produced. The revenue generated by these orders enabled Whitney to expand his Mount Eden premises and purchase more modern machinery from Britain. To help finance this rapid expansion, Whitney transformed his private company into a limited liability, the Colonial Ammunition Company Limited, in 1888. Realising that further opportunities existed on the Australian mainland, Whitney established an ammunition factory at Footscray, Melbourne, in 1890 and quickly secured the contracts for the supply of ammunition to all the mainland Australian colonies. On 23 September 1897 an explosion killed three women workers and destroyed part of the factory. By 1917 the Colonial Ammunition Company had a staff of over 2,000 and was considered important not only for the defence of Australia and New Zealand but also for their economies.
In addition to supplying military ammunition to the governments of Australia and New Zealand, the company diversified into sporting ammunition. Whitney himself was described by Whitmore as a 'good sportsman and a wonderful shot'. By 1900 the Colonial Ammunition Company satisfied demand in Australia and New Zealand for quality, quantity and competitive pricing of sporting cartridges. A further diversification for the company involved research and development of ammunition. In 1903, for example, Whitney invented and tested a sharp-pointed .303 bullet which had a flatter trajectory than was otherwise available. This antipodean achievement was several years ahead of developments at Woolwich, Britain's leading arsenal. The Colonial Ammunition Company was easily able to meet the demands of the First World War when both Australia and New Zealand required millions of rounds for their expeditionary forces.
In 1921 the Australian government negotiated a lease for the Melbourne factory (and subsequently purchased it in 1927). At the same time Whitney re-established the New Zealand holding as a private concern; he operated under the same name by purchasing its assets from the parent company. After John Whitney's retirement his second son, Cecil, became managing director, while one grandson became general manager and another became manager.
Harriet Whitney died at Wenderholm, Waiwera (their home for over 30 years), on 6 February 1917, and John died aged 96 at Remuera, Auckland, on 6 September 1932. Whitney was a prominent and devout Anglican. He built a church at Waiwera and provided its endowment, and gave funds for the upkeep of the Clevedon cemetery, where he was buried.