He was born in Chicago, and brought up near Sheridan, Wyoming in the United States, where his parents farmed. He was educated in England, at Farnborough, at Winchester College and at Balliol College, Oxford. He then farmed at Farleigh Wallop in Hampshire.
He was Conservative Member of Parliament for the Basingstoke constituency from 1929 to 1934. He stepped down and caused a by-election in March 1934 (Henry Maxence Cavendish Drummond Wolff was elected). At this point he was in the India Defence League, an imperialist group of Conservatives around Winston Churchill, and undertook a research mission in India for them.
His exit from party politics was apparently caused by a measure of disillusion, and frustrated ambition.
In 1936 he sent for auction at Sotheby's the major collection of unpublished papers of Isaac Newton, known as the Portsmouth Papers. These had been in the family for around two centuries, since an earlier Viscount Lymington has married Newton's great-niece.
The sale was the occasion on which Newton's religious and alchemical interests became generally known. Broken into a large number of separate lots, running into several hundred, they became dispersed. John Maynard Keynes purchased many significant lots. Theological works were bought in large numbers by Abraham Yahuda. Another purchaser was Emmanuel Fabius, a dealer in Paris.
During the 1930s, and until 1943 when he became Earl, Wallop was generally addressed and known by the courtesy title Viscount Lymington.
He was a member of and important influence on the English Mistery, a society promoted by William Sanderson and founded in 1929 or 1930. This was a conservative group, with views in tune with his own monarchist and ruralist opinions.
A split in the Mistery left Wallop leading a successor, the English Array. It was active from 1936 to the early months of World War II, and advocated "back to the land. Its membership included A. K. Chesterton, J. F. C. Fuller, Rolf Gardiner, Richard de Grey, Hardwicke Holderness, Anthony Ludovici, John de Rutzen, and Reginald Dorman-Smith. It has been described as "more specifically pro-Nazi" than the Mistery; Famine in England (1938) by Lymington was an agricultural manifesto, but traded on racial overtones of urban immigration. Lymington's use of Parliamentary questions has been blamed for British government reluctance to admit refugees.
He edited New Pioneer magazine from 1938 to 1940, collaborating with John Warburton Beckett and A. K. Chesterton. The gathering European war saw him found the British Council Against European Commitments in 1938, with William Joyce. He joined the British People's Party in 1943. The English Array was not shut down, as other organisations of the right were in the war years, but was under official suspicion and saw little activity.
Freeman Dyson encountered as a schoolboy the new Earl of Portsmouth, while harvesting during the war:
The Kinship in Husbandry, which he also founded with Rolf Gardiner, was one of the precursors of the later Soil Association. It recruited Edmund Blunden, Arthur Bryant, H. J. Massingham, Walter James, 4th Baron Northbourne, Adrian Bell and Philip Mairet.
After the war he moved to Kenya, where he lived for nearly 30 years.