The contract, which will run for a further five years, is worth more than £75m .
Mitie will work at over 100 buildings across Britain, predominately in the corporate office estate, including the main campus at The Quadrant:MK in Milton Keynes.
Mitie will be responsible for delivering a comprehensive range of services including fabric and engineering maintenance, energy management, security, cleaning, mailroom & couriers, helpdesk, waste and pest services.
Nigel Bunclark, Director Workplace Management at Network Rail said: “After a competitive procurement process we are looking forward to continuing our relationship with Mitie under the new contract.
“It is an opportunity to work together to advance our strategy of providing great workplaces that are value-for-money, fit-for-purpose and sustainable.
“Mitie understands our vision to give our people efficient, effective and engaging workplaces.”