The operator will occupy the top two floors of Hudson Quarter, a sustainable development which offers more than 11,000 square feet of commercial space.
The site was once the main trunk route for the York and North Midlands Railway and trains to London via Derby and Birmingham, designed in 1840 by George Hudson.
Peter Liney, chief executive of Great Rail Journeys, said the operator wanted to invest in a "more flexible, creative and collaborative" environment.