Osborne has been given the design and build contract, having recently complete its £14.5m makeover of Clapham Junction station in south London.
At Dartford a new concourse, ticket office and facilities will make it easier and more pleasant for passengers to get around, especially at peak times, said Network Rail.
Rail office buildings in front of the station will also be demolished, to make way for more parking. Staff in those offices will relocate to the first and second floors of the new building.
The upgrade is being funded jointly by the Homes & Communities Agency through Dartford Borough Council (£6.073m) and the government’s national stations improvement programme (£1m).
Work is expected to start in September and be completed before the end of 2012.
Vince Lucas, Southeastern’s service delivery director added: “Dartford is one of our busiest stations and deserves an environment to match. This project will help provide our passengers with a better experience when travelling by train and help area around the station. We will be working hard with Network Rail to ensure that there is minimal disruption to our services.”
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 use the station during the 15 month construction period.