Harold Gladstone Miller was born on 15 May 1898 in Masterton to Nellie Stores and her husband, Tobias Miller, a shop assistant. He was educated at Masterton District High School, where he captained both the First XV and First XI. He then entered Victoria University College, Wellington, where he gained an MA degree with first-class honours in philosophy. Miller won the Senior Scholarship in economics in 1918 and was actively involved in student life. Awarded a Rhodes Scholarship in 1920, he entered Balliol College, Oxford.
While in England, Miller married a fellow New Zealander, Edith Race Davies, at Camborne, Cornwall, on 11 July 1923. The following year the couple returned to New Zealand where Miller lectured at the Wellington Teachers' Training College and for the WEA in Timaru. In 1928, at the age of 29, Miller was appointed to the position of librarian at Victoria University College, a post he held for the next 38 years.
Miller's development as a librarian was much advanced by his tenure of a Carnegie Corporation of New York travelling fellowship in 1932–33 at the library school of the University of Michigan at Ann Arbor. He was a member of a distinguished group: Alice Minchin, librarian of Auckland University College; Clifford Collins, subsequently librarian of Canterbury University College; and Alister McIntosh, at that time on the staff of the General Assembly Library in Wellington but later to become secretary of the Department of External Affairs.
Undaunted by the paucity of resources which awaited him on his return from the United States, Miller proceeded to develop at Victoria a collection of some depth and strength. He was by upbringing and inclination a scholar librarian and the collection he built was in the nature of a scholar's library. He sought to create a collection that would meet not only immediate needs but also those of future generations across a wide range of disciplines. He achieved this through the judicious purchase of individual titles, greatly assisted initially by a succession of Carnegie Corporation grants, and by the acquisition of existing libraries. Notable among these were a substantial collection of books from the Nelson diocesan library, and the Brancepeth collection, a private library formed to meet the needs of Brancepeth station employees, donated to the Victoria University Library by the Beetham family of Wairarapa in 1966.
Miller's firm belief in the enduring nature and value of library collections shaped his views on the role of a university library. As his contemporary Clifford Collins observed on his retirement, Miller thought it 'a university library's duty…to acquire the important books, costly though they might be and little used', taking over responsibility 'just about where its users as personal bookbuyers with reasonably long pockets had to stop'. By the end of his career in the 1960s the general perception of the role of a university library had begun to change, with a growing recognition of the pressing need to offer a range of undergraduate services. Miller himself provided a means by which such change might be effected by planning a new building into which the library moved in 1965, a year before his retirement in 1966.
A librarian by profession, Miller retained his interest in historical scholarship, publishing, among other works, a history, New Zealand, in 1950, and Race conflict in New Zealand, 1814–1865 in 1966. He was also much immersed in church affairs throughout his life. Raised as a Methodist, he embraced the Anglican faith while at Oxford. A student of the Oxford Movement, Miller saw himself as a defender of Anglican orthodoxy in his membership of the Wellington diocesan synod and the General Synod, and in his role as a pamphleteer for the Selwyn Society and a columnist for the monthly Anglican newspaper Church and People. Both learned and witty, and taking a delight in controversy, he was the intellectual leader of New Zealand Anglo-Catholics.
Harold Miller was a man of strongly held views who enjoyed argument and was always ready to provoke it. But he was also open-minded, tolerant and generous to others. His contribution to librarianship and historical scholarship in New Zealand was recognised by the award of an honorary doctorate of literature from Victoria University of Wellington in 1966. Shortly before the death of his wife, Edith, in 1976, Miller moved to Auckland, where he died at Selwyn Village on 4 March 1989, survived by his son and two daughters.