By 1876, the Metropolitan Railway (MR) and District Railway (DR) had constructed the majority of the Inner Circle (now the Circle line), reaching Aldgate and Mansion House respectively. The companies were in dispute over the completion of the route as the DR was struggling financially and the MR was concerned that completion would affect its revenues through increased competition from the DR in the City area. City financiers keen to see the line completed, established the Metropolitan Inner Circle Completion Railway in 1874 to link Mansion House to Aldgate. Forced into action, the MR bought-out the company and it and the DR began construction of the final section of the Inner Circle in 1879. On 6 October 1884, the final section of the Inner Circle was opened along with Cannon Street station. Initially the station was served by trains from both companies as part of circular Inner Circle service but various operational patterns have been used during the station's life. The Inner Circle service achieved a separate identity as the Circle line in 1949 although its trains were still provided by the District or Metropolitan lines.
The Underground station underwent major reconstruction at the same time as the main line station, with the work being completed in 2012. From 14 December 2014, the station's opening hours changed significantly, with the station opening on Sundays and no longer closing early in the evenings. The station previously had restricted opening hours because it primarily served the local financial services sector, so there was low demand for services outside office hours. The station has cash machines, wi-fi, payphones, a bridge and lifts.
Connections: National Rail (Cannon St.). Circle Line. London Buses routes 15, 17, 521 and heritage route 15H and night routes N15 and N47 serve the station.