In 1782, after his father's death in the preceding year, Alexander Stewart, probably using some money from the inheritance, bought the Ards House and some surrounding lands near it on the shores of Sheephaven Bay near Dunfanaghy, County Donegal, for £13,250 from William Wray and started to live there.
[1] Mary was the niece of Sarah Frances Seymour-Conway, the first wife of Alexander's eldest brother Robert, Lord Londonderry.
Alexander and Mary had among other children three sons who reached adulthood: Stewart was appointed High Sheriff of Donegal for 1791–92.
He was elected for the County Londonderry constituency of the Irish Parliament in 1800, sat for County Londonderry for one month and then exchanged it for the borough of Thomastown for which he sat until Irish Parliament was abolished due to the Acts of Union in 1801.
[16] He thus served as "a family stopgap" who "supported [the Earl of Liverpool's Tory] government silently".