The project will see a new second platform and fully-accessible footbridge with lifts added to the East Lothian station.
The new infrastructure will provide increased capacity and improve operational flexibility at Dunbar.
Detailed design-work will now begin for the project. Engineering work is expected to start next summer with the new infrastructure completed in early 2020.
Matthew Spence, Network Rail route delivery director for Scotland, said: “The new platform, which will be fully accessible, will mean extra capacity at Dunbar and create opportunities for more services to stop in the future. We look forward to working closely with Amco to deliver this important enhancement for the town.”