Lowther was the third and youngest son of John Lowther, 1st Viscount Lonsdale and his wife Katherine Thynne, daughter of Sir Henry Frederick Thynne, 1st Baronet (ancestor of the Marquesses of Bath).
[1] Reputed one of the handsomest men of his day, Lowther was first returned to Parliament for Cockermouth in a by-election on 21 July 1721 following the death of Lord Percy Seymour.
At the 1722 election, Sir Wilfrid Lawson took the Cockermouth seat himself, while Lowther was returned through his own family's interest for Westmorland.
[1] In 1726 Lowther obtained a position as commissioner of the revenue for Ireland, which he resigned in 1734, apparently out of pique at not receiving any greater preferment.
He was supposed to have had a hand in stoking the discontent of his elder brother, Viscount Lonsdale, which led the latter to resign as Lord Privy Seal in 1735.