The project to create a new secondary school building and sports hall was procured through the EFA framework.
A site, close to Maple Cross, will be the new home for The Reach Free School, which is currently based at Wolsey Business Park.
The new location will also mean that the school is located at the centre of its catchment area, which covers Mill End, Rickmansworth and Maple Cross.
The plans include a major investment in local highways infrastructure, including on-site parking spaces.
Chris Tredget, managing director of Willmott Dixon in the Northern Home Counties, said that the project followed the company’s recent contract to deliver Hertswood Academy in Borehamwood.