The state government has awarded a $45.9 million contract to Pindan Construction to build a new Governor Stirling High School in Woodbridge.
Finance Minister Simon O'Brien said the old buildings would be demolished within a few weeks.
To allow for construction, staff and students have been relocated to two separate schools.
Students in years 8-10 are at Midland Primary School and students in years 11-12 are at Cyril Jackson Senior High School.
The new school will include a two-storey main building and a single storey centre dedicated to Aboriginal student learing.
"As the site is limited in its physical capacity, it has taken innovative planning to incorporate the many facilities in the design," Mr O'Brien said.