Koscielny has made 163 appearances for the Gunners since arriving from Lorient four years ago and signed his previous deal as recently as 2012.
The France centre-half's form this season has seen him linked with Bayern Munich and Paris Saint-Germain, but he has now joined defensive partner Per Mertesacker in extending his Emirates contract.
"I am very proud to have reached agreement with the club on a new contract," the 28-year-old told the Arsenal website.
"I have enjoyed four great years at Arsenal already, and I look forward to continuing to help the team in the years to come."
Arsene Wenger said: "Laurent has proven himself to be an outstanding player since joining us in 2010 and has showed his quality once again this season.
"I am delighted he has decided to commit his future to the club."
Koscielny's partnership with Mertesacker has left club captain Thomas Vermaelen on the sidelines for much of the current season.
He is the eighth member of Arsenal's first-team squad to sign a new contract this term.