Newton Wallop, 6th Earl of Portsmouth (19 January 1856 - 4 December 1917), known as Viscount Lymington until 1891, was a British Liberal politician who sat in the House of Commons from 1880 until 1891 when he inherited the Earldom and took his seat in the House of Lords.

Lymington was born in Whitchurch, Hampshire, Portsmouth, the eldest son of Isaac Newton Wallop, 5th Earl of Portsmouth, and his wife Lady Eveline Alicia Juliana, daughter of Henry Herbert, 3rd Earl of Carnarvon. He was educated at Balliol College, Oxford. Lymington was a J.P. for Hampshire and Devon, and a Deputy Lieutenant.

Lymington was elected Member of Parliament (MP) for Barnstaple at a by-election in February 1880,[2] a seat he held until 1885 when representation was reduced to one member under the Redistribution of Seats Act 1885. At the 1885 general election, he was the elected MP for South Molton and held the seat until 1891.[3] In the latter year he succeeded his father in the earldom and took his seat in the House of Lords. From 1905 to 1908 he served as Under-Secretary of State for War in the Liberal administration of Sir Henry Campbell-Bannerman.

Lord Portsmouth married Beatrice Mary Pease, only child of Edward Pease of Darlington, in 1885. He died in December 1917 at Whitchurch, aged 61, and was succeeded in the earldom by his younger brother John. The Countess of Portsmouth died in 1935.