Arthur Paul Harper, known for much of his life as AP or APH, was born in Christchurch on 27 June 1865, the eldest child of Joanna Dorothea Dyke Acland-Troyte and her husband, Leonard Harper, a barrister, explorer and later MHR. His grandfather, Henry Harper, was the first Anglican bishop of Christchurch and the family were members of the Canterbury establishment. Harper's early childhood included private schooling and many outdoor activities at Ilam, the family home. After a trip to England in 1878 he attended Christ's College, Christchurch, until the end of 1883. From October 1884 his education continued at Oxford University, where he completed a BA in 1887. He then read law at the Inner Temple in London and was called to the Bar in 1888.
After returning to Christchurch in 1889 Harper enjoyed a variety of social and sporting activities, and developed an interest in photography. While in Europe a friend had challenged him to try climbing in the Alps. Harper was greatly attracted to the mountains and they were to dominate much of the rest of his life. On expeditions in the Southern Alps between 1890 and 1892 he was struck by the lack of civilisation and the number of unclimbed peaks. Both contrasted markedly with Europe and seemed to offer more challenging opportunities for young New Zealanders, though Harper himself soon preferred exploration to climbing.
Climbers such as George Mannering enlisted his support, and as part of an effort to encourage mountaineering, Harper combined with Mannering and Malcolm Ross in 1891 to form the New Zealand Alpine Club. Harper chose to model it on the Alpine Club of London, which promoted the interests of the gentleman amateur rather than professional mountain guides. These class-based divisions were to restrict the development of both the club and mountain climbing in New Zealand for many years.
In the early 1890s Harper's life took a significant turn. He had probably been intending to work as a lawyer in his father's firm, but Leonard Harper left New Zealand in July 1891. Over the next two years it emerged that the firm was bankrupt and that about £200,000 had been embezzled. This was an economic disaster and a social disgrace for APH, who had to work hard to help sort out both the firm's and his family's affairs. On a trip to England for this purpose in 1892, however, he enjoyed meeting various prominent figures, including Oscar Wilde and the Arctic explorer Fridtjof Nansen, and undertook more climbing in Europe.
Back in New Zealand, family business continued to dominate Harper's life until he escaped to the West Coast late in 1893. There he joined the Department of Lands and Survey as an assistant to the veteran explorer Charlie Douglas. Between 1893 and 1895, often working alone because of Douglas's ill health, Harper explored the Franz Josef and Fox glaciers, and several major rivers. He helped fill a number of gaps in the West Coast survey, and began a lifelong interest in glaciology.
In 1895 Harper surveyed West Coast gold reserves for the New Zealand Midland Railway Company. The following year he began practising as a barrister and solicitor in Thames. Returning to the South Island in 1900, he prospected and reported on West Coast mining propositions, then practised law in Greymouth from 1903 to about 1907. Over the following years he expanded his interests in coalmining, becoming general manager and owner of the North Brunner Coal Company. By this time Harper had a wife and family to support, having married Marion Florence Campbell at Papanui on 5 April 1899; they had three sons and two daughters. From about 1912 the family lived in Wellington, where APH worked as a sharebroker and was secretary of the right-wing New Zealand Welfare League.
An exploratory trip into the upper Waimakariri River in 1912 was Harper's only mountain expedition in many years, but his interest remained. He attempted to revive the now-defunct Alpine Club in 1914, but the restrictions he imposed on membership, as well as the onset of the First World War, meant that it did not function effectively until the 1920s.
Harper was president of the New Zealand Alpine Club from 1914 to 1932, but only towards the end of that period did his views of climbers and climbing become less élitist. He returned to the mountains from 1926 to 1928 to introduce his second daughter, Rosamond, to mountaineering. Now in his mid 60s, Harper began to meet a new generation of climbers. They found his approach too cautious and he never fully understood them, but he appreciated their achievements and in his own way encouraged them. He continued to attend Alpine Club meetings, camps and hut openings until near the end of his life.
In the 1930s A. P. Harper began to take on more public roles in mountaineering and conservation. He was instrumental in the formation of the Federated Mountain Clubs of New Zealand in 1930, and served as its president (1933–34) and patron (1952–54). He encouraged the establishment of reserves and national parks and became a member of the Honorary Geographic Board of New Zealand in 1934, and of the Tongariro National Park Board in 1938. Elected an honorary member of the English (1932) and American (1937) alpine clubs, Harper was president of the New Zealand club again for its jubilee year in 1941. In the 1940s he gave radio talks on the mountains, and he was president of the Forest and Bird Protection Society of New Zealand from 1948. Two years later he was awarded the Loder Cup for encouraging the protection of New Zealand's flora, and in 1952 he was made a CBE for his services to conservation and mountaineering.
A. P. Harper died in Wellington on 30 May 1955, survived by two daughters and a son. He had enjoyed a long, full life, but there were sad personal times: one of his sons died in 1918, his wife in 1938, and his youngest son in 1943 (killed in action during the Second World War). Nor was his life untouched by controversy, for his definite opinions and class-based thinking alienated others and were sometimes detrimental to the development of mountain clubs and their activity. However, there is no doubting his lasting love for the mountains, and his strong advocacy was significant in the development of New Zealand mountaineering.