Stagecoach has been selected as the preferred bidder to provide commuter and shuttle bus services for Sellafield Ltd.
The company will take over the contract on 1 April 2020.
Passengers will see current services maintained and improved. Fares, where charged, will remain unchanged.
People employed on the current contract will be transferred to the new supplier via the TUPE process.
Efficiency improvements are forecast to save £9.3m over the lifetime of the contract.
The winning bidder was chosen following a rigorous and competitive tender process.
Its tender was scored the highest across four criteria: delivery, safety, cost, and innovation.
Steve Bostock, Sellafield Ltd site director, said:
"Our commuter, shuttle, and park and ride bus services have been a huge success.
"Hundreds of people are using the service, reducing the number of vehicles entering the Sellafield site and helping us deliver our mission.
"Congratulations to Stagecoach on winning this contract. I look forward to working with the company to maintain and enhance our bus services.
"I’d like to thank our current supplier Reays for their excellent service. I wish them continued success in the future."
Rob Jones, managing director of Stagecoach Cumbria and North Lancashire, said:
"We are delighted to have been awarded the Sellafield contract. This is an exciting opportunity for us to grow our business.
"We have a longstanding history in the area; our national head offices operated from Whitehaven for a number of years with Cumbrian staff instrumental in building the company.
"We look forward to working with Sellafield to continue delivering excellent bus services."