Macleay was born on Ross-shire, Scotland, eldest son of William Macleay, provost of Wick. Alexander had a classical education, before relocating to London and becoming a wine merchant with his business partner William Sharp - after whom his first son was named. In 1795 he was elected a fellow of the Linnean Society of London, also serving as its Secretary, and was also appointed chief clerk in the prisoners of war office. When the office was linked with the Transport Board after war broke out, Macleay became head of the correspondence department and by 1806 secretary. The Board was abolished in 1815 and Macleay retired on an annual pension of £750.
Macleay's chief natural history interest was entomology, principally lepidoptery, and he possessed the finest and most extensive collection then existing of any private individual in England and possibly the world. This included the British Collection of John Curtis now housed in Melbourne, Australia. In 1813, he was elected a foreign member of the Royal Swedish Academy of Sciences.
On 14 June 1825, Macleay was appointed Colonial Secretary for New South Wales. He arrived in Sydney in January 1826, with his wife Eliza, 9 of his 10 surviving children, and his extensive collection. He was soon working twelve hour days and in July 1826 was eventually made a member of the Executive and Legislative Councils. Originally residing at the Colonial Secretary's House in Macquarie Place, Macleay was granted land at Elizabeth Bay by Governor Ralph Darling, where he constructed Elizabeth Bay House and laid out an extensive botanic garden.
He was also very active beyond his scientific pursuits and was the foundation president of the Australian Club.
- "About the Macleay Museum". University of Sydney. 2006-06-12. Archived from the original on 24 June 2007. Retrieved 2007-07-03.
- 'McLeay (Macleay), Alexander (1767 - 1848)', Australian Dictionary of Biography, Volume 2, MUP, 1967, pp 177–180.
- Serle, Percival (1949). "Macleay, Alexander". Dictionary of Australian Biography. Sydney: Angus and Robertson.
- Macleay, Alexander, Australian National Herbarium
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- McLeay, Alexander (1767-1848) National Library of Australia, Trove, People and Organisation record for Alexander McLeay