The £7m revamp will modernise station facilities and provide better journeys for more than 3m passengers every year.
Osborne will need to demolish the existing station to make way for a new three-storey structure where building work is scheduled to start next August.
Before that the firms will build a new concourse and ticket office and more parking bays at the front of the station.
Dave Ward, Network Rail’s route director for Kent, said: “We want more people to choose to travel by train, which means we need to give passengers the end-to-end journey experience they expect.
“This starts with providing a station environment and modern facilities which meet their needs.”
The station will remain open to passengers throughout the construction with no disruption to the train services.
A temporary station entrance and ticket office will be created to allow passengers to continue safely using the station during the 15 month construction period.
Proposed timescales for key elements of the work:
Sept 11 – Oct 11: construct temporary ticket office
Nov 11 – Mar 12: Improvements to platforms
Apr 12 – July 12: Install new waiting shelter and staff accommodation on plat 1 & 2
Aug 12 – Oct 13: construct new station building and extend canopies
Nov 13 – Jan 14: extend car parking & landscaping