William Blomfield was born in Auckland on 1 April 1866, the son of Emma Watts Collis and her husband, Samuel Blomfield, a carpenter. The family moved to Thames the next year. In 1880 they returned to Auckland where William's uncle, the prominent artist Charles Blomfield, found him a job in a paint and picture shop. Shortly afterwards he began to train as an architect.
William had been interested in drawing and caricature from a very early age, despite little encouragement from his immediate family. He sold his first cartoon to the Observer, an Auckland-based weekly, receiving five shillings for his caricature of a legislative councillor. In 1884 he welcomed the opportunity to exchange the formal strait-jacket of architecture for comparative freedom as an articled pupil on the artistic staff of the New Zealand Herald.
Blomfield worked at the Herald in the days before newspaper photography, when artists sketched their impressions of great and calamitous events. The highlight of his three years at the Herald was a daring trip made in June 1886 to inspect the desolation caused by the eruption of Mt Tarawera. He was sent at very short notice, in the clothes he was wearing and with £12 for expenses, to find out if the Pink and White Terraces really were destroyed. Travelling by train, trap and borrowed horse, he encountered deeper and deeper volcanic ash and experienced repeated earth tremors before reaching Lake Rotomahana. There he and his guide narrowly escaped injury when a bank collapsed behind them. The news that the terraces were destroyed was telegraphed back to Auckland and featured prominently in the Herald.
In 1887 Blomfield accepted an invitation to become an all-purpose wood engraver, litho artist and cartoonist for the Observer's successor, the New Zealand Observer and Free Lance. Usually known by its original name, the paper was the first of a lively new breed of illustrated weeklies that reflected the country's blossoming social, sporting and cultural interests. Blomfield's cartoons with their bold 'Blo' signature soon became a distinctive feature.
On 11 December 1889, in Auckland, William Blomfield married Anna Maria Adams. By this stage he had met William Geddis, a sub-editor of the Auckland Star, and in 1892 the two pooled their meagre resources and purchased the Observer. The paper's sole assets were its copyright, cases of dilapidated type and some rickety furniture. Three years later they helped establish the Spectator, a similar Christchurch weekly. In 1900 they began the New Zealand Free Lance in Wellington, and the Auckland paper became the New Zealand Observer. Although Blomfield's involvement with the Free Lance was short-lived, the Geddis family controlled the Wellington weekly until it closed in 1961. Geddis gave up his interest in the Observer in 1910, but Blomfield was to remain a substantial shareholder until his death.
Blo specialised in sketching the protagonists in the more spectacular and salacious Auckland court cases, and in 1913 this led to his involvement in a famous court action. In September that year an issue of the Observer carried an editorial and two Blomfield cartoons, all commenting on the behaviour of the presiding judge in a divorce case. One cartoon, captioned 'Justice is not blind', showed Justice W. B. Edwards, who had been showing obvious bias towards a pretty woman witness, peering slyly from under a blindfold at the lady in the box. Contempt of court proceedings were issued, but the case was dismissed by the full Bench of the Supreme Court in Wellington. It is uncertain whether the crowd and the band that escorted Blomfield down Queen Street to the railway station on his way to Wellington was a tribute to his popularity or an expression of concern about Justice Edwards's erratic courtroom behaviour.
The Observer flourished until the late 1920s. Circulation and advertising dipped sharply during the depression, but the weekly fought back strongly with the popular formula of Blo cartoons and contributions from writers such as Robin Hyde and A. R. D. Fairburn. Blomfield was the Observer's cartoonist for 51 years. Every week for decades he drew a full-page, tabloid-size cover cartoon, two or three further full-pages, and another six to eight small block cartoons or caricatures. While this volume of work is unlikely to be matched by another cartoonist, his much more substantial contribution was to the development of cartoon art in New Zealand.
His style was sometimes dismissed disparagingly as 'rush and ready', but along with his younger brother John Blomfield and E. F. Hiscocks, he was one of the first to shrug off the prim, static, relentlessly cross-hatched style of the early New Zealand cartoonists. Blomfield's line continued to loosen as he grew older and there was sometimes a semi-abstract feel to his cartoons. He was often careless and haphazard about details and background, but his work had a vitality and visual flow that links him directly to today's leading cartoonists.
The Blomfields lived at Takapuna for many years where William was a prominent citizen, serving (1914–21) as the borough's second mayor and as a director of several mining and commercial enterprises. He was working at his cartoons until his death on 2 March 1938, in Auckland. He was survived by five children; his wife had died in 1935.