The deal has bee awarded under the Southern Construction Framework to refurbish the school’s Grade Two* listed Hare Hall building.
Work includes providing a new food technology room, extra science laboratory, further additional classroom space and larger canteen plus a separate external sports hall.
The project also includes construction of a temporary school facility which will house pupils from Hare Hall while work is carried out.
Work is set to start this week and be completed by autumn 2021.
Willmott Dixon is working with a team that includes Vincent & Gorbing Associates as architects and ARCADIS Design & Consultancy as project manager.
Hare Hall was originally designed by James Paine in 1768-69 for John Wallinger, a cork and stone merchant of Colchester. The building has been the Royal Liberty School since 1921.