Jack, 25, was announced as Swans co-captain on Friday and will share the skipper's job with veteran Jarrad McVeigh.
Jack replaces superstar Adam Goodes, who surprisingly stepped down after four seasons sharing the captaincy.
While Goodes, 33, stepped down as skipper, the decorated champion signed a new contract through to the end of next season.
Jack also celebrated his elevation into captaincy with a new contract until the end of 2015.
Jack has played 114 Swans games and is the son of rugbly league legend Garry.
Swans 2012 premiership coach John Longmire hailed the amazing progression for one of the AFL's now most reputed on-ball stars.
"Kieren is a pretty unique story and it is a great credit to him and just how hard he has worked that he now gets the opportunity to lead the club,” Longmire said.
"He has come off the rookie list and joins Jarrad McVeigh as co-captain of the club he barracked for as a kid.
"Over the past few years we have seen Kieren develop enormously as player, but also as a leader.
"I’m sure he will continue to grow into the captaincy role but I’m really confident he and Jarrad will be a fantastic combination to guide our group."
Longmire also paid enormous tribute to the remarkable service Sydney has had from the brilliant and record-breaking Goodes.
"Adam has been a tremendous leader of our club for a long time and while he won’t be a captain, he will still play an important role in our leadership group," he said
"The club fully supports Adam’s decision to stand down after four years as co-captain and think it is a great show of faith from him in our younger leaders."
Longmire and his match committee have continued a tried and proven policy of joint captains, introduced under 2005 Swans premiership coach Paul Roos.
Jack is a remarkable success tale after he was plucked as a Sydney local recruit through the 2007 rookie draft from a school days rugby league background.
The relentlessly tough on-ball play-maker and clearances expert was a pivotal performer in Sydneys' stunning premiership victory over Hawthorn last season with 14 possessions and nine tackles.
He won Sydney's fairest-and-best in 2010 and also finished fourth in last year's highly consistent premiership season.