The deal will keep him with the London club until the end of the 2014-15 season.
The 27-year-old graduate of the Harlequins Academy made his senior debut in 2004 and has since made 89 appearances for the current Premiership champions.
He has represented England at Under 19 and 21 levels and was a member of the England Saxons team that played in the 2009 Churchill Cup tournament.
"There are people who epitomise what a club is about and what a team is about and Mark is one of those players," said Conor O'Shea, Harlequins director of rugby.
"He gives his heart and soul for Harlequins and having made the transition from tight head to loose head so seamlessly he is someone we are going to rely on heavily in the years to come if we are to attain the goals we all aspire to. Everyone involved with Harlequins is delighted that Mark will continue to develop and push on wearing the Harlequins colours."
Lambert added: "When I signed for Quins at 18 I could never have dreamt of being here for over a decade. In my years at the club I've been through deep lows and massive highs, both personally and collectively.
"Last season was more than a dream come true and I feel privileged to have played my part in it, but I look forward to contributing more in future successes. I still feel I have much to prove to myself and others in the quartered shirt. I will relish that challenge."
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