Adam Simmonds has announced that part of the Wootton Hall Park site is to be acquired by the the Education Funding Agency for the Wootton Park School.
The school aims to meet the demands of the increasing population in and around Northampton.
It will have a crime science specialism and is due to open in September 2016.
The school says on its website it aims to "establish a regional, national and ultimately international reputation for the quality of education".
Mr Simmonds confirmed that Northamptonshire Police will leave their current Wootton Hall headquarters following public consultation
The decision comes two weeks after the PCC formally approved the construction of two new Northamptonshire Police buildings in the north of the county - the Northamptonshire Police Investigation Centre and Northern Accommodation Building, situated just off the A43 next to the A6003 between Kettering and Corby.
It is anticipated that building work will be completed by spring 2017, while the new premises will provide work space for approximately 350 staff.
Mr Simmonds said: "Moving to new premises will save in excess of Â£40m over the next 25 years, which will allow us to keep more frontline officers on the streets, keeping Northamptonshire safe.
"There could be no better legacy to Northamptonshire Police's work at Wootton Hall than to open a new free school on the site with a specialised, policing and public service-focussed curriculum."
Chief Constable lice, Simon Edens, added: "Policing is changing and is likely to keep changing, at a faster pace, in the future, and I am not satisfied that all of our current buildings, including Wootton Hall, are fit for purpose."
Northamptonshire's police and crime commissioner has agreed in principle to sell part of the force headquarters to house a new free school in Northampton.