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,[2] 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.

[4] 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.

He was soon working twelve-hour days and on 17 July 1825 was nominated to the New South Wales Legislative and Executive Councils, holding both positions until December 1836.