The League Two final will take place on May 28 while the League One final will be on May 29.
The play-off’s have been moved from Wembley due to the Champions League final.
Football League chairman Greg Clarke said: “We are thrilled to have the opportunity to play these exciting winner-takes-all occasions at one of the great stadiums in world football.
“We are equally pleased that we are able to take the npower Football League play-offs to the north west, an area that has been at the heart of professional football since its very origins.”
Manchester United chief executive David Gill added: “We are delighted Old Trafford has been chosen to stage these two finals.”
