Walter Lawry Buller was born at the Wesleyan mission, Newark, at Pākanae, Hokianga, New Zealand, on 9 October 1838, the son of Jane Tonkin Martin and her husband, James Buller. He married Charlotte Mair at Whāngārei on 24 April 1862; they had four children. He died at Fleet, Hampshire, England, on 19 July 1906.
Buller's parents emigrated to Australia in 1835 from struggling middle class circumstances in Helston, Cornwall, hoping to join a Wesleyan mission in the South Seas. James Buller was both devout and forceful; he was accepted as a missionary soon after arriving at the Mangungu Wesleyan mission, Hokianga, from Sydney, in April 1836, served briefly at Pākanae and then for 15 years at Tangiterōria, Kaipara. He was then minister in Wellington, Christchurch, Auckland and Thames, becoming president of the Australasian Wesleyan Conference in 1864.
Walter Buller, the second of 10 children, grew up at Tangiterōria and was educated at the missionaries' Wesleyan College in Auckland. After the family moved to Wellington in 1855 he became native interpreter in the Magistrate's Court, but his obvious ability and energetic self-promotion soon brought him advancement in the Native Department. In 1862, when the network of magistrates in Māori districts was expanded under Governor George Grey's 'new institutions', he was appointed resident magistrate in Manawatū. There he became involved in assisting Isaac Featherston's land purchasing for the Wellington provincial government. In 1865 he was transferred to Whanganui, but Featherston had him seconded back to complete the purchase of the disputed Rangitīkei–Manawatū block; this was eventually done over Ngāti Raukawa protests.
From his schooldays Buller had a passion for natural history, especially ornithology, which then meant the collection and describing of specimens. He advanced by his own initiative and by contacts with men such as Dr Thomas Ralph, James Hector and George Grey. In 1858, when only 19, he was admitted as a fellow of the Linnean Society of London. His first important scientific paper was written for the New Zealand Exhibition at Dunedin in 1865. He was originally invited to contribute a mere appendix to an essay by Richard Taylor, but made the most of the opportunity; his Essay on the ornithology of New Zealand entirely eclipsed Taylor's and established him as an authority on the subject, especially after he sent copies abroad and engaged in a vigorous debate with Otto Finsch of Bremen over the species he had named as new.
By 1871 Buller had assembled the materials for a comprehensive treatise on the ornithology of New Zealand, and negotiated a government grant and leave on half pay to publish it in London. To supplement his income there he was also appointed secretary to Featherston, who had become agent general. There were accusations of patronage, especially when it became known that Buller also intended reading law at the Inner Temple; but although he stretched his leave and eventually had to resign his magistrate's position, his time in London was very successful. With Finsch's help he received a doctorate in natural history from the university of Tübingen in 1871. He was called to the Bar at the Inner Temple in 1874. His book, A history of the birds of New Zealand, published in 1873, won him wide acclaim and, to the chagrin of more established rivals for honours, the CMG in 1875.
On his return to New Zealand in 1874 Buller practised as a barrister, specialising in Native Land Court business. He made two unsuccessful attempts to enter politics, being defeated in elections for Manawatū in 1876 and Foxton in 1881. His legal practice, however, was so lucrative that in 1886 he retired and returned to London as commissioner for the Colonial and Indian Exhibition; he was promoted KCMG for his services. Nor had he neglected science, although his torrent of papers in the Transactions of the New Zealand Institute slowed after 1879 when he gained his 'blue riband of science', a fellowship of the Royal Society of London. The enlarged edition of his History, published in 1888, became a New Zealand classic, especially for J. G. Keulemans's chromolithographic plates, which are still the standard images of New Zealand birds.
After business difficulties brought him back to New Zealand in 1890, Buller established a country home at Lake Papaitonga, Horowhenua, on land leased and purchased from Te Keepa Te Rangihiwinui. He thus became drawn into the tangled dispute over the Muaūpoko tribal estate at Horowhenua, especially after the minister of lands, John McKenzie, accused him of defrauding Muaūpoko. In the ensuing legal battle McKenzie was no match for Buller and all his charges failed, but Muaūpoko and Te Keepa paid dearly. The government took Muaūpoko land for the costs of a commission of inquiry; and Buller, while defending his own interests, acted throughout as Te Keepa's counsel and charged him accordingly. Eventually, in 1899, Buller won the freehold of his beloved Papaitonga, but left immediately for England. Although expressing nostalgia for New Zealand in his Supplement to the 'Birds of New Zealand', published in 1905, he was, finally, quite the London gentleman.
Buller held the prevailing view that the native plants, birds and people of New Zealand would inevitably be displaced by the more vigorous European immigrants. The Māori, he thought, 'are dying out and nothing can save them. Our plain duty as good compassionate colonists, is to smooth down their dying pillow.' Similarly, he generally rejected as hopeless T. H. Potts's ideas for the conservation of both native forests and birds. However, in 1891 he backed the governor, Lord Onslow, in his successful plea for statutory protection of birds such as the huia, and the creation of sanctuaries at Resolution and Little Barrier islands. But despite advocating these moves, Buller remained equivocal about their value and continued to take specimens of the rarer birds for his own and other collections.
Buller completely dominated New Zealand ornithology, while remaining a gentleman naturalist rather than a professional scientist. But despite his New Zealand birth, or perhaps because of it, the success he mainly strove for, and won, was at Home, in England.