Construction work will restart immediately on the 20,000 sq m Riverside South scheme after JP Morgan confirmed its commitment to staying in London.
The US bank said it would work with Canary Wharf Group to bring the mothballed development to street level after acquiring the former Lehman Brothers building in the Docklands business zone for £495 million.
The development agreement has been extended to October 2016.
The firms stopped building the costly headquarters earlier this year, triggering speculation JP Morgan would axe the development, which it bought for £237m in 2008, due to negative sentiment towards banks.
JP Morgan chief executive Jamie Dimon said: “This acquisition is a long-term investment and represents part of our continued commitment to London as one of the world’s most important financial centres.”