Stewart was the younger brother of Robert, 1st Marquess of Londonderry, Castlereagh’s father, on whose interest he sat for a month in the Irish parliament for county Derry in 1800 before transferring to Lord Clifden’s borough of Thomastown. In September 1800 he was spoken of as a likely parliamentary candidate for Donegal, where he had resided for 18 years.
Stewart, conscious of what he called ‘the family interest entrusted to my care’,
