Francomb, released by the Canaries this summer, spent three impressive months on loan with the Dons over the first half of last season.
Boss Neal Ardley duly made signing the 21-year-old one of his top priorities this summer and he has won the race for his signature ahead of a couple of League One clubs.
"We were very sorry to lose George when he went back to Norwich because he was probably the highlight for us in a struggling team at the time," Ardley told AFC Wimbledon's official website.
"I really enjoyed working with him then because you could see the quality he had.
"As soon as I knew the player would be leaving Norwich I threw my hat into the ring. I spoke to his agent in early May because I knew I would have to do a bit of work to get him. I had to try and put the budget in place so that we could make an offer that could bring George back here.
"I am delighted that George has joined and he is a great signing for the club."
And Francomb, himself, is targeting a promotion challenge next term after watching the Dons narrowly avoid relegation from League Two.
He added: "I did have a couple of League One clubs interested in signing me, but I wanted to come here.
"If I did not believe that Wimbledon had ambition then I would not have returned. Hopefully I can hit the ground running and we can be challenging at the other end of the table. I am delighted to have signed here and I cannot wait to get started."