St. Mary's was a station on the District and Metropolitan lines of the London Underground. It was located between Whitechapel and Aldgate East stations, in the East End of London.

The District line is a London Underground line running from Upminster in the east and Edgware Road in the west to Earl's Court in west London, where it splits into multiple branches. One branch runs to Wimbledon in south-west London and a short branch, with a limited service, only runs for one stop to Kensington (Olympia). The main route continues west from Earl's Court to Turnham Green after which it divides again into two western branches, to Richmond and Ealing Broadway.