He will be formally honoured at a meeting of councillors on October 14, said Trafford Council.
Sir Alex is also being recognised by the local authority with a road near Old Trafford stadium having its name changed from Waters Reach to Sir Alex Ferguson Way.
Sir Alex said: "I am delighted to accept this honour from Trafford Council. When I arrived at Old Trafford in 1986 I had little idea of the journey that awaited me. Over quarter of a century later, to receive the Freedom of the Borough of Trafford and to have a part of Trafford carrying my name is truly humbling."