Alexander Stewart (26 March 1746 – August 1831) was an Irish landowner and Member of Parliament.
He was the son of Alexander Stewart of Mount Stewart by his wife Mary, sister and heiress of Robert Cowan of Bombay.
His elder brother was Robert Stewart, 1st Marquess of Londonderry.He was appointed High Sheriff of Donegal for 1791–92 and in 1800 was elected to the Irish Parliament as the MP for County Londonderry.
On 1 July 1814 his nephew Sir Charles Stewart, the MP for County Londonderry, was raised to the peerage as Baron Stewart, and Alexander Stewart was elected to replace him on 19 July, as "a family stopgap" who "supported [the Earl of Liverpool's Tory] government silently".
He sat for the constituency until the 1818 general election, when his son was elected, having come of age.