Isaac Newton Wallop, 5th Earl of Portsmouth DL JP(11 January 1825 – 4 October 1891) was a British Peer and the son of Newton Fellowes, 4th Earl of Portsmouth and Lady Catharine Fortescue.

Newton Wallop, 6th Earl of Portsmouth JP, DL, styled Viscount Lymington until 1891, was a British Liberal politician but then joined the Liberal Unionist Party in 1886. He later switched back to the Liberal Party to serve as Under-Secretary of State for War under Sir Henry Campbell-Bannerman from 1905 to 1908.