Fifteen hundred jobs will be created during the building of the Strule Shared Education campus in Omagh, County Tyrone.
The Education Minister, Paul Givan, launched the construction phase of the £375m project during a visit to the town.
It is the single largest education project in Northern Ireland and is expected to be completed by September 2028.
It will see 4,000 pupils from five secondary schools joining Arvalee Special School on the site of the former Lisanelly Army Barracks.
While each school will maintain its own identity and ethos, there will be shared areas including performance spaces and sports facilities.
The army vacated the 120-acre site in 2007 and demolition was completed in 2016 when Arvalee Special School relocated.
There have been many delays in completing the vision of the shared education project.
Mr Givan said it was “huge for the people of Omagh and I believe Northern Ireland”.
“This is the single, biggest education project that we are taking forward.”
Mr Givan said the construction would generate more than £1bn for the local economy.
Local company Woodvale Lowry was awarded the contract to build Strule last month.