The Addicks confirmed the loan deal for the England U21 international at 11.40pm, with twenty minutes left until the deadline.
Cranie joins until the end of 2008, and should be joined at the Valley by former Addick Linvoy Primus, but that deal will only go through once Charlton and Portsmouth can agree on the length of loan.
Any deal is expected to be confirmed after September 8th, when the 'emergency' loan window opens.