The France international has tied himself to the north London club for the foreseeable future, with manager Arsene Wenger hailing his "exceptional" progress since joining
The France international, 26, has impressed since arriving in north London from Lorient in summer 2010 and has been rewarded with an improved deal.
"Laurent has been outstanding for us over the last two seasons," Gunners boss Arsene Wenger told the club's official website.
"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.
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With injuries disrupting Wenger's back line in recent years, Koscielny has become a mainstay at the Emirates Stadium and scored the winner against West Brom on the final day of last season to guarantee the club Champions League football in 2012-13.
"I'm delighted to have reached agreement with the club," the centre-back enthused. "I have had a fantastic time here and look forward to an exciting future with Arsenal."