More detailed plans will now be drawn up by Kier, which has been awarded a contract to build the school.
The new school at Beaulieu in Chelmsford would provide an initial 900 secondary school places from September 2019, growing to 1,200 in future years.
Together with an adjoining 420-place primary school and 56-place Early Years building, which have already been approved and are set to open for September 2018, it would operate as the county’s first all-through school.
Subject to planning processes, work on the new secondary school building should now start as soon as July and be completed in January 2019.
Essex County Council is also planning a new 900-place secondary school in Colchester, which will be built on the former Alderman Blaxill School site in Paxman Avenue.
This project has now also moved a step closer after an outline business case for the plans was approved by councillors.
Subject to planning processes, it is now hoped demolition of the existing school buildings could start in September, with building work starting in February 2018 and being completed in advance of September 2019.