According to the age given on his death certificate William Meluish was born probably in 1822 or 1823. An advertisement in the Nelson Examiner in February 1859, soon after he arrived in New Zealand, announced that he had a photographic studio in Bridge Steet, Nelson, and was 'late of Crystal Palace'. Apart from the approximate time of his birth and his likely London origins, nothing is known for certain about his early life. He married, but the date and place of marriage and his wife's birth name are unknown.
It is believed Meluish first arrived in New Zealand in December 1858. He spent some 14 months in the Nelson area. As well as his photographic premises in Nelson he opened a gallery at the Star and Garter Hotel in Richmond in May 1859, and travelled to Collingwood in December 1859. During this period he advertised that he had changed from daguerreotypes to the wet-collodion process, printed on paper and by which 'any number of copies can be produced, from one sitting'. As well as portraits he took photographs of the town of Nelson, and signed examples of his views are held at the Nelson Provincial and the Otago Early Settlers museums.
In February 1860 Meluish announced his departure from Nelson. He leased a property in central Dunedin, and in August an advertisement in the Otago Colonist announced: 'Views of Dunedin now ready…from 2s 6d each, at Meluish's Photographic Gallery, next to Oddfellows' Hall, Princes Street'. Photographs of the gallery show advertisements and signs in the windows indicating he was also an importer of 'photographic apparatus and materials'. In 1861 he took over the photographic studio of James Wilson; two years later advertisements indicate his studio was now on the corner of Dowling and Princes streets.
Illness caused Meluish to give up photography in the mid 1860s, but he maintained his importing business until his departure from the country in 1870. In 1868 he gave what was heralded as the first lantern lecture to be held in New Zealand or Australia, in the newly opened post office building in Dunedin.
Meluish took portraits of leading Dunedin citizens and photographs of city residences, but his outstanding contribution to the documentation of Dunedin's history was his photographing of cityscapes from the same viewpoints at regular, annual intervals. Taken during the early 1860s, a period of great prosperity and growth brought about by the Otago gold discoveries, they show rapid changes. This project was later continued by one of Meluish's pupils, Joseph Weaver Allen, by D. L. Mundy who took over his studio in 1864, and from 1873 by the Burton brothers.
Meluish was successful in business, and also a public-spirited and generous man. As early as 1861 he had invested in property in Dunedin, purchasing for £340 the section on the south-west corner of the Octagon. Here he opened the Octagon Family Hotel of which he was the proprietor between 1862 and 1864. When this building was destroyed by fire in 1867 and a fellow photographer, James de Maus, lost his uninsured studio and equipment in the fire, Meluish organised a round robin and generously contributed himself to re-establish Maus.
Meluish returned to live near the Crystal Palace in London and died there on 28 November 1888 at the age of 65. His wife, Emma, inherited his considerable estate: in 1882 his freehold land in Dunedin had been valued at £8,820, and this alone places him in the top five per cent of wealth holders in the colony at that time.