Work is set to start on site this month, with project being handed over in February 2022.
The new school buildings will expand capacity by 150 to 1,500 pupils aged 11 to 16.
Interserve Construction regional director Phil Shaw said: “This is a really important opportunity for us and the local community. As we venture into uncertain times it is really important we provide opportunities to rebuild the economy through local employment.
“Our appointment by the Department for Education to build the new Saddleworth School further strengthens our position as one of the leading construction companies serving the UK education sector and follows the team’s recent appointment to build the special needs Halcyon Way and Prospect House schools, also in Oldham.”