The 24-hour service will run on Fridays and Saturdays between New Cross Gate and Dalston Junction, and will be extended to Highbury & Islington next year.
It follows the success of the Night Tube, which has already seen more than 6.5 million journeys since its launch last year.
Mayor of London Sadiq Khan said: 'Our Night Tube services have been a real success right across the Capital, so I'm delighted to announce that we'll be bringing the Night Overground to the East London line later this year.
'It will provide huge benefits to Londoners and visitors to our city, helping those working hard through the night and all those out enjoying everything London has to offer, as well as creating jobs and boosting our economy.'
The East London section of the Overground route serves an area popular for museums, restaurants, bars and night spots. Trains will help people working shifts in hospitality and service sectors, and those who live in outer London, by substantially reducing their journey times.
It will connect with the Night Tube at Canada Water on the Jubilee line and, from next year, Highbury & Islington on the Victoria line.
This year marks the tenth anniversary of the London Overground. Since TfL took over suburban rail routes in 2007, passenger numbers have increased six-fold and the network has become one of the most reliable railways in the country.