The Financial Conduct Authority (FCA) will be leaving Canary Wharf and moving to a new £2.6billion development in Stratford.
With detailed planning consent already secured for both buildings, construction will start this summer, ready for occupation to begin in 2018.
FCA acting chief operating officer David Godfrey said: “The International Quarter offers a compelling mix of an excellent building and facilities, value for money, sustainability and the right infrastructure to meet our future needs.
"We look forward to bringing all our London staff together in this exciting new development.”
Transport for London will move into another of the office blocks, meaning together, an estimated 6,500 TfL and FCA staff will occupy the development’s new generation of offices.
The International Quarter – which, at a total of 4million sq ft, is one of the largest new commercial developments in Europe.
Once completed, more than 25,000 people will work at the development each day.