William Francis Drummond Jervois was born, probably on 10 September 1821, at Cowes, Isle of Wight, England, and was baptised there on 16 October. He was the eldest son of Lieutenant Colonel (later General) William Jervois and his wife, Elizabeth Maitland. After early schooling at Dr Burney's Academy, Gosport, and Barry's school, Woolwich, he entered the Royal Military Academy in 1837. Graduating two years later, he was commissioned as a second lieutenant in the Royal Engineers. He attended the School of Military Engineering at Chatham from 1839 to 1841.
Following service in the Cape of Good Hope, Jervois commanded a Royal Engineers company at Woolwich and Chatham from 1849 to 1852 before working on the defences of Alderney. On 19 March 1850 he married Lucy Norsworthy at London; they were to have three daughters and two sons. In 1855 he assumed command of the Royal Engineers in the London military district, and the following year was appointed to the War Office with responsibility for designing Britain's harbour defences. As director of works for fortifications from 1862 to 1875 he oversaw their construction.
Jervois, who was made a CB in 1863, also became an authority on the defences of the British Empire – and of some of its potential enemies. During the American civil war he visited the United States twice, and sketched the harbours of Portland and Boston while disguised as an artist. He reported on the defences of British North America, and travelled widely to inspect defences elsewhere. In 1871 he was approached for defence advice by Julius Vogel, New Zealand's colonial treasurer, who was in London on financial business. Jervois obliged by drawing up a report based on charts, in which he recommended a system of heavy guns at the main ports at a cost of £44,000. An impressed Vogel made arrangements whereby the colonial government might keep in touch with him unofficially.
Made a KCMG for his colonial services in 1874, Sir William Jervois was appointed governor of the Straits Settlements in April of the following year. In 1877 he was promoted to the rank of major general, and was asked to survey the defences of the Australian colonies. He had completed the survey for New South Wales and was embarking on the task for Victoria when he learned that he had been transferred to South Australia, a move which reflected Colonial Office unhappiness with his interventionist approach in Malaya. Although Premier Harry Atkinson had hoped to have Jervois report on New Zealand's defence needs, his successor, Sir George Grey, was much less interested in the provision of harbour defences and refused to send the government vessel to fetch him. Ironically, a war scare in 1878 induced Grey's ministry to urgently acquire heavy guns with which to arm the ports – New Zealand's first major external defence procurement – on the basis of British advice which followed Jervois's 1871 report to Vogel.
These guns had still not been emplaced when Jervois, now a lieutenant general, was appointed governor of New Zealand. He assumed office on 20 January 1883. The government willingly accepted his offer of advice on harbour defence provision. With the help of an officer of the Royal Engineers, Major Henry Cautley, brought out for the purpose, Jervois visited the ports in question and refined his earlier views, outlining them in an address to the New Zealand Institute in October 1884. In essence Jervois reaffirmed the pre-eminence of heavy guns over new weapons such as the mine and the torpedo, and proposed that New Zealand supplement the ordnance acquired in 1878 with the most modern six-inch and eight-inch guns. These weapons were ordered during another more serious war scare early in 1885. Late in March Jervois convened a meeting at Government House in Wellington which established an emergency defence programme. After the scare subsided Jervois oversaw the permanent fortification of the harbours, his leading role being recognised in the naming of the fort on Lyttelton's Rīpapa Island after him. Always welcomed by the government, his influence was nevertheless criticised by some who looked askance at the expensive defences taking shape at the main ports even as the colony's financial woes mounted.
Although his constitutional position left him with little discretion, Jervois carried out his duties conscientiously and without fuss. One of his sons, Major John Jervois, served as his private secretary from January 1886. As a practical man he related well to colonial politicians, but could be firm when necessary. In 1886 he would have nothing to do with suggestions by Robert Stout and Julius Vogel for a dissolution of Parliament. On imperial issues he was prepared to act vigorously to restrain his government: during December 1884 he drew some criticism for preventing it from sending the colonial secretary aboard the government steamer Hinemoa to investigate a plea from Malietoa, King of Samoa, and many other leading Samoans, for British annexation. Following the Tarawera eruption in 1886 he took the initiative in establishing a committee to consider means of providing relief to the survivors.
Jervois played a prominent role in the social life of New Zealand, serving as patron of various cultural and sporting bodies and travelling extensively. He took an especial interest in the New Zealand Institute, over which he presided, and in 1888 fulfilled a long-standing aspiration when he was made a fellow of the Royal Society of London. Such was his popularity that he departed from New Zealand in March 1889 to the accompaniment of many 'sincere and heartfelt expressions of regard and esteem'. The feeling of mutual regard and the attraction of the country itself were reflected in Jervois's claim to have given serious consideration to living permanently in New Zealand.
In retirement Jervois continued to have an influence on defence matters, both in England and abroad. He served as a member of a consultative committee on coastal defence duties, and became colonel commandant of the Royal Engineers in 1893. In New Zealand, which he revisited in 1892, his views were still valued. Richard Seddon used authoritative comments by him in favour of the existing harbour defences in his dispute with the commandant of the New Zealand forces, Lieutenant Colonel F. J. Fox, early in 1894.
William Jervois died on 17 August 1897 after being involved in a carriage accident at St Mary Extra, Southampton, and was buried near Virginia Water, Surrey. His wife had died two years before. The names of a glacier in Fiordland and one of Wellington's leading streets recall his association with New Zealand.