The Abbey Wood to Paddington section will open to passengers on May 24, although initially trains will not run on Sundays or call at Bond Street.
Once the route is open, services in the central London section will run every five minutes between 6.30am and 11pm, but a full timetable will not be in place until May 2023.
Passengers wishing to travel the length of the line will need to change at Paddington or Liverpool Street, depending on their destination, until next year.
When the line reaches Whitechapel, it will branch off into two separate directions. One of these will head southeast and terminate at Abbey Wood.