The 24-year-old England World Cup hopeful's new deal will keep him at the Twickenham Stoop until at least 2014.
Robshaw, capped by England in 2009, skippered his country in tour games against the Australian Barbarians and New Zealand Maori last summer.
He is a Quins academy product, and in his first season as club captain Quins have reached the Amlin Challenge Cup final, when they will play Stade Francais in Cardiff on Friday week.
Robshaw, a former Premiership player of the season, said: "Harlequins are a great club, and one which I think is on the verge of great things in the coming years.
"We have a squad with a great mix of youth and experience, and we are trying to play a brand of rugby that will excite and challenge."
Quins rugby director Conor O'Shea added: "Chris Robshaw embodies everything this club is and wants to be about.
"At still only 24, Chris wants to push on for both Harlequins and England, two goals that are well within his compass."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The entire All Blacks apparel line has been updated for 2013/14. Check out the New Zealand All Blacks polo.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Gilbert Blitz 8S rugby cleat is a great cleat at a great price of $69.99. Get a new pair of cleats today.
A cool looking all black rugby cleat with the high performance adidas is known for. Get in the Gear!
Wear the crest of the British and Irish Lions on your t-shirt. A great look for the summer.
The All Blacks Performance t-shirt is black with hints of blue from the training jersey. Very Cool.
The New Zealand All Blacks training jersey for 2013/14. Get in the Gear!
The USA Rugby Pro Alternate rugby jersey is perfect for any fan of the Eagles. Get yours to wear during the summer Test matches.
The NEW All Blacks 2013/14 jersey has arrived at World Rugby Shop. Dare to wear the colors of the All Blacks.