The midfielder made over 230 appearances for the Dons before heading for Plymouth in a £200,000 deal in January 2008.
He has now returned to Pittodrie and the 30-year-old has expressed his delight at linking up with Craig Brown's side.
"It's been a difficult time at Plymouth with their off the field problems but I feel I'm a better player for the experience," he told the club's official website.
"I know other clubs were interested but the family love it in the North East and it's fantastic to see so many familiar faces."
Dons boss Brown added: "His availability was too good an opportunity for us to refuse so we are delighted he has committed himself to Aberdeen.
"His versatility is the main attribute he has. He is able to play in a number of different positions. He will be a great addition to the squad."