The extension will use part of the existing London Fenchurch Street - Tilbury line east of Barking, diverging onto a new 1.6km electrified branch at Renwick Road to reach the two-platform Riverside terminus.
Barking Riverside is the largest brownfield housing development in east London, with planning permission for 10,800 homes as well as healthcare, retail, and leisure facilities.
The £263m extension is fully funded and the developers of the site, Barking Riverside Limited, will provide £172m towards the project with the remainder coming from Transport for London (TfL).
Balfour Beatty, Carillion, and Volker Fitzpatrick were shortlisted for a contract to build the extension in December 2016 and TfL expects to issue an invitation to tender to the three bidders in the autumn. Preliminary works will begin before the end of the year and the project is due to be completed in 2021.
The Gospel Oak - Barking line is currently being electrified and TfL has ordered a fleet of eight four-car Aventra EMUs from Bombardier to replace the class 172 DMUs currently used on the route.