Alexander Kingcome Turner was born in Auckland on 18 November 1901, the son of Joseph Hurst Turner, a teacher, and his wife, Gertrude Kingcome Reid, the daughter of a leading Methodist minister. He attended Mount Eden School and Auckland Grammar School. When he was 11 his father died, leaving Alexander's mother and her four sons in a state of poverty.
In 1917 Turner won a university entrance scholarship and enrolled the following year at Auckland University College. He graduated BA (1921), MA with first-class honours in economics (1922), and LLB (1923). Meanwhile, he had become a legal clerk in an Auckland law firm, and there spent six years learning to behave 'as a lawyer and a gentleman', in the course of which, in 1923, he was admitted as a barrister and solicitor. On leaving in 1926 Turner practised for 10 years on his own, and then as a partner in what became Turner, Kensington and Haynes. As a lawyer he was known for his industry, concentration, incisiveness, courtesy and fairness.
Turner's working commitments left him little time for social and other pursuits, but he enjoyed golf and music and achieved success as Auckland table tennis champion in 1926 and Auckland mixed doubles tennis champion in 1931. He was married in Wellington on 21 March 1934 to Dorothea Frances Mulgan, the daughter of Alan and Marguerita Mulgan. Dorothea became an eminent author, critic and Greek scholar, and a highly regarded weaver.
While practising at the Auckland Bar, Turner was active in academic circles. He was president of the Auckland University College Students' Association (1928), president of the Auckland district Court of Convocation of the University of New Zealand (1933), and a member of the Auckland University College Council (1935–51). He represented the college as a governor of Massey Agricultural College from 1944 to 1953 and his interest in agricultural research led to a Carnegie Corporation travel grant in the United States in 1949.
In 1952 Turner was made Queen's counsel and on 29 June 1953 he was appointed judge of the Supreme Court of New Zealand. After serving on provincial courts he became senior Auckland judge. On 30 August 1962 he was elevated to the Court of Appeal, and the Turners moved to Wellington. Turner served on the Court of Appeal at a key stage in its early development, and he was to remember his time with fellow Appeal judges Alfred North and Thaddeus McCarthy as among the happiest and most successful periods of his life. From 1 February 1972 until his retirement 17 months later he was president of the court.
Alexander Turner acquired a reputation as one of New Zealand's most distinguished jurists by virtue of his wide knowledge, painstaking research, analytical ability and lucid exposition. He was a scholar who delighted in grappling with ideas and words in written form. His statements were quoted with approval by the Privy Council, and a number of his judgements, notably The Queen v. Convery and Naniseni v. The Queen, were to be highly influential in New Zealand law. He was made a Knight Bachelor in 1963, a privy councillor in 1968 and KBE in 1973, and he was awarded an honorary LLD by the University of Auckland in 1963.
During his time on the Bench Turner rewrote the classic English texts by George Spencer Bower, The law relating to estoppel by representation (he produced another edition in 1977) and The doctrine of res judicata, and then The law of actionable misrepresentation in 1974. In December 1973 he was made editor in chief of the New Zealand Commentary on Halsbury's Laws of England, and he held this post for the next 19 years. He also served as a director of Butterworths and organised the writing of numerous New Zealand legal texts. In 1990 he co-authored The law relating to actionable non-disclosure.
Alexander Turner died in Auckland on 7 July 1993, survived by his wife and three children. He is regarded as one of New Zealand's finest expositors of the law, as reflected in his judgements and in his publications.