Earl of Portsmouth is a title in the Peerage of Great Britain. It was created in 1743 for John Wallop, 1st Viscount Lymington, who had previously represented Hampshire in the House of Commons. He had already been created Baron Wallop, of Farleigh Wallop in Hampshire in the County of Southampton, and Viscount Lymington, in 1720, also in the Peerage of Great Britain.
The third Earl declared himself King of Hampshire and his brother had him declared insane.
The fourth Earl represented Andover and Devonshire North in Parliament. In 1794, he assumed by Royal licence for himself and his issue the surname and arms of Fellowes only.
The fifth Earl resumed, without Royal licence, the family surname and arms of Wallop.
The sixth Earl represented Barnstaple in Parliament as a Liberal.
Oliver Henry Wallop, the eighth Earl, had moved from England to the United States, and had been living the life of a rancher in Sheridan, Wyoming, at the time of the death of his older brother, the seventh Earl. Known as O.H. Wallop, he had served two terms a state representative in the Wyoming Legislature. He had become an American citizen in 1891, and was allowed to take his seat in the House of Lords only after renouncing American citizenship.
The ninth Earl sat as Conservative Member of Parliament for Basingstoke.
The tenth Earl, who succeeded in 1984, is the only son of Oliver Kintzing Wallop, Viscount Lymington (1923–1984).