Stuart Alexander Donaldson was the first Premier of the Colony of New South Wales. He held the offices of Premier and Colonial Secretary from 6 June 1856 until 25 August 1856 - a period of just two months and 20 days. He was succeeded by Charles Cowper, who was to occupy the office of Premier on five different occasions. Donaldson was never to be Premier again.

Donaldson was born on 16 December 1812 in London, England. He entered his father's firm at the age of 15 and was sent first to Mexico (1831-1834), for business training, and then to Sydney, where he arrived in 1835.

In 1848 Donaldson was elected a member of the first Legislative Council of New South Wales. Between February 1848 and April 1859 he served seven terms in the Council and in the Legislative Assembly, representing the County of Durham, the Sydney Hamlets, and Cumberland (South Riding). He returned to London between 1841 and 1844 and also travelled to England in 1853-1854. As well as Premier, he also served as Colonial Treasurer (1856-1857) and was a Commissioner for Railways in 1857.

Donaldson returned to England for the last time in June 1859 and was knighted there in 1860. Following his return, he unsuccesfully sought election to the British House of Commons on two occasions. He had four sons and one daughter. He died on 11 January 1867 at Carleton Hall, near Holmrook , in Cumberland, England.