The title Baron St John de/of Basing was created twice in the Peerage of England.
On 29 December 1299 John St John was summoned to parliament. On the death of the third baron the barony fell into abeyance in 1347. Only fourteen years later, the abeyance was terminated in favour of Isabel Poynings, née St John, in whose right Lucas de Poynings, her husband, was summoned. And at the death of the fifth baron, who was the son-in-law of the third Earl of March, the barony fell into abeyance again.
The second creation was in 1539 for William Paulet, who was later created Earl of Wiltshire and Marquess of Winchester, with which titles the barony has remained united, although the Marquesses of Winchester were also Dukes of Bolton from 1689 to 1794, when the dukedom became extinct.