Mills will remain in the red and white until at least the end of 2023, an extra five years added to his previous commitment which was due to end in 2018.

He goes past teammates Lance Franklin and Isaac Heeney, and Essendon's Michael Hurley, who are all signed until 2022.

It's the second time in three months the Swans have invested heavily in their youth, following highly-rated Heeney's five-year deal signed in December off the back of just his second AFL season.

"It was an extremely easy decision," Mills said.

"I feel in debt to the club because they've put so much time, effort and resources into me as a 13, 14-year-old boy to where I am today. I love the club at the moment and where it's heading and the people involved.

"The direction and the people and the culture that's all combined at the club is somewhere that I really want to be. Hopefully we have a lot of success along the way."

Mills grew up on Sydney's northern beaches and came through the Swans Academy before he was drafted to the club at the end of 2015.

Melbourne initially made a play for Mills with their third selection, but the Swans were able to match the bid using four higher-round draft picks.

He played 22 games in his debut season, primarily as a half backman, but injured his hamstring in the qualifying final loss to the Giants before returning to play in the grand final defeat to the Western Bulldogs.

His re-signing caps off a big week for the club which announced on Tuesday that goal-kicking great Tony Lockett would return in a mentoring capacity.

"I used to love Plugger, I don't really remember it too much but my Mum used to say how much I used to love Plugger," Mills said.

"He was a great player and a huge Sydney name really. He carried the club for a while there with his big presence and goalkicking ability."