He sat in the Irish House of Commons as MP for Belfast, and held office as Third Serjeant-at-law and later as a Baron of the Court of Exchequer (Ireland).

Apart from his legal and political career, his main interest in life was in developing the town of Balbriggan.

He opened factories there, began a cotton manufacturing industry, and encouraged the breeding of horses.

Reportedly he became something of a bore on the subject: it was said facetiously that only some great preoccupation could cause him to go for more than fifteen minutes without mentioning Balbriggan pier.

[3] Alexander served briefly as his father's replacement as MP for Belfast, but died prematurely in 1808.