The ruins of Lesnes Abbey lie between Abbey Road and Lesnes Abbey Woods at Belvedere, formerly part of Kent but now in the London borough of Bexley in SE London. In the Middle Ages the river Thames and its marshland were much closer to the abbey.

The ruins include the restored foundations of the abbey church. The church was set out during the founder's lifetime (d. 1179), and consisted of an aisled nave, transepts with three eastern chapels on each side, and an aisleless presbytery. The total internal length of the church was 234 ft. and 66 ft. across the transepts; this makes it one of the largest Augustinian naves in Britain. The abbey was built of Kentish ragstone, flint and chalk.

The ruins were excavated by the Woolwich Antiquarian Society in 1909, up to 1930 by Sir Alfred Clapham, and between 1939 and 1951 by E C Elliston Erwood for the London County Council who owned them at that time.

The abbey of St Mary and St Thomas the Martyr was founded by Richard de Luci, Chief Justiciar of England, for Augustinian Canons in 1178. The abbey was suppressed by Cardinal Wolsey in 1524, when all the buildings were demolished, except the Abbot's Lodgings. The mansion into which the Lodgings had been converted was also taken down in 1844.

The chancel arch base with quirk and cyma moulding looks Gothic, even though it underlies apparently Romanesque material. Given that the abbey was founded in 1178, was this perhaps a Transitional or Early Gothic element.

For a possible reset capital from the abbey, see the CRSBI entry for Erith, St John the Baptist.