The agent, known by his code name Stakeknife, has been linked to more than 50 murders.
The probe into the crimes is to be funded by the PSNI but staffed by external officers – it will be led by the Chief Constable of Bedfordshire Police.
Investigators will also examine possible crimes by IRA members, other agents, and army or police handlers that emerge during the course of their work.
The investigation is expected to take at least five years and cost almost 40 million Euro.
