There is evidence, from flint finds, of occupation of a site, known as Westbury Sleight during the Mesolithic period,[2] which fieldwork during 2007 suggested was a platform cairn with field banks of Bronze Age date.

[3] In 1969 traces of an infilled cave were discovered in a limestone quarry which produced numerous bones from extinct animals and flakes of flint and chert.

The 'fortification' may have been the Iron Age fort above the neighbouring village of Rodney Stoke; or the sub-circular enclosure around a British church or monastery; or around the lord of the manor's hall, now Court House Farm.

The station, known as Lodge Hill, apparently to avoid confusion with Westbury in Wiltshire, is now an industrial estate providing employment for the village.

For local government purposes, the village falls within the Somerset Council unitary authority area, which was created on 1 April 2023.

Westbury-sub-Mendip falls within the county constituency of Wells and Mendip Hills, which has been represented in the House of Commons of the Parliament of the United Kingdom by Tessa Munt of the Liberal Democrats since 2024.