Longmire – who was contracted until the end of the 2015 season – commenced as senior coach in 2011 and has led the club to three successive finals series, including the 2012 premiership.
Sydney Swans Chairman Andrew Pridham said the club was happy to secure Longmire for a further two seasons beyond his current contract.
“John has proven an outstanding senior coach since taking on the role in 2011," he said.
“His work with the playing group and vision for our team is second to none.
"On and off the field, the club is in great shape and shoring up John's future at the club until 2017 is another great step forward.”
After 200 matches and a premiership as a player with North Melbourne, Longmire joined the Swans as an assistant coach at the start of the 2002 season.
In 2007 he was appointed coaching coordinator and succeeded Paul Roos as senior coach for the start of the 2011 season.
Longmire led the Club to the 2012 premiership in just his second season as senior coach and followed up with a preliminary final berth in 2013 despite an injury plagued season for the playing list.
Swans CEO Andrew Ireland said extending Longmire's tenure was an important step for the future.
"The club believes that having an eye for the future is equally as important as the here and now, so having John commit to at least the end of 2017 gives he and General Manager of Football, Dean Moore the opportunity to build the football department for not only this season, but seasons to come," he said.
“John is an incredibly hard working coach who has overseen finals campaigns in each of his three seasons in charge.
"One of his strongest assets is his commitment to improving the football program each and every year.
“This is a strong and united playing group that continually sets high standards for themselves, and much of that is owed to John’s leadership.
“We look forward to John leading the team to success in 2014 and beyond," Ireland said.
