The City branch of the Northern line had been closed since early January to allow major works to be completed at Bank where a new wider southbound platform has been created.
"I’d like to thank our customers for their patience during this closure," said Stuart Harvey, chief capital officer at Transport for London.
"The improvements we’re making at Bank station will be finished by the end of this year and will totally transform customer journeys through the station. Anyone who’s familiar with Bank station will know how its labyrinthian layout can be confusing and time-consuming to navigate.
“Northern line customers now have a new, wider southbound platform and spacious customer concourse. The countdown is on for completing the rest of this major upgrade which is one of the largest and most complicated subterranean railway complexes in the world.”
During the closure of the Bank branch new lifts have been installed at Borough Underground Station and enabling works for the future Elephant & Castle station upgrade have been carried out.
The last day of service for the route 733 bus between Moorgate and Oval – which was introduced specifically for the Bank branch closure period – was Friday 13 May.