Watts, a former No.1 draft pick, has signed a new deal with the Demons which will keep him there until the end of 2016.
While the jury remains out on Watts, his signature is clear vindication of the Demons' decision to break the bank for the Sydney premiership coach to drag them out of the abyss.
On arriving at Melbourne earlier this month, Roos had made it clear he wanted to keep the 22-year-old, who was off contract.
Watts' ability to play forward, back or on the ball - and a talent which has been seen only in glimpses in his five AFL seasons - would have made him highly sought by rival clubs.
He said Roos' decision to join the Demons had been significant in his decision to stay.
And Watts revealed Roos had told him he was likely to play as a big-bodied midfielder in 2014, rather than forward or back where he has played most of his football.
"To have someone of his stature and even just to be able to talk to him for five minutes and see his visions of where we're going and what kind of person he is, that made the decision a lot easier," Watts told melbournefc.com.au on Tuesday.
"(It's) a big relief and it brings a lot of happiness. I'm stoked to get it done and I can look forward to next year now.
"I love the club and want to stay there."
Watts had said in July - soon after Mark Neeld's mid-season sacking - his preference was to remain at the Demons despite interest from elsewhere.