The 26-year-old France international joined Arsenal from Lorient in 2010 and has since established himself as a key member of Arsene Wenger's side.
A statement on the club's website read: "Arsenal football club is delighted to announce that Laurent Koscielny has agreed to sign a new long-term contract."
No details about the length of Koscielny's new contract were given. Koscielny has started 85 games for Arsenal over the last two years - no other player has started more at the club - and last year he earned his first call-up to the France squad.
Since then, the former Guingamp and Tours centre-back has taken his tally of Les Bleus caps to four, the most recent of which came in the Euro 2012 quarter-final defeat to Spain, where he played the full 90 minutes in a 2-0 loss.
Wenger said: "Laurent has been outstanding for us over the last two seasons. When you consider that until 2009 he was playing in Ligue 2 in France and that he is now performing at the very top level in the Premier League and for his country, the development that he has shown has been absolutely exceptional.
"Laurent is a top-class player and I am very pleased he has decided to commit his future to the club."
Koscielny added: "I'm delighted to have reached agreement with the club. I have had a fantastic time here and look forward to an exciting future with Arsenal."
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