Lowther was a Member of Parliament for over twenty years and served as Lord-Lieutenant of Westmorland and Cumberland.In 1784 he was raised to the Peerage of Great Britain as Baron Lowther, of Lowther in the County of Westmorland, Baron of the Barony of Kendal in the County of Westmorland and Baron of the Barony of Burgh in the County of Cumberland, Viscount Lonsdale, Viscount Lowther and Earl of Lonsdale, with normal remainder to the heirs male of his body.He was succeeded in the barony and viscountcy of 1797 according to the special remainder by his third cousin once removed, Sir William Lowther, 2nd Baronet, of Little Preston.He was a prominent Tory politician and notably served as Postmaster General and Lord President of the Council.In 1841 he was summoned to the House of Lords through a writ of acceleration in his father's junior title of Baron Lowther.His son from his second marriage, William Lowther (who was born posthumously), sat as Member of Parliament for Carlisle.Richard Lowther, younger son of the first Baronet, was Member of Parliament for Appleby.His son Robert Lowther, the father of the fifth Baronet, was a Member of Parliament and Governor of Barbados.