He joins director of rugby Conor O'Shea, head coach John Kingston, skills coach Collin Osbourne and forwards coach Tony Diprose in agreeing a new deal; the quartet all signed extensions earlier this year.
Forty-year-old Mapletoft, capped by England in 1997, represented Quins during his playing career, and returned to the club in 2010 and he is now contracted until 2015.
Having helped O'Shea's side to Premiership glory against Leicester at Twickenham in May, he is delighted to have extended his stay at the Stoop.
The former England Under-20 coach said: "When Conor O'Shea offered me the opportunity to extend my stay with the club, it was a very easy decision.
"Harlequins is a fantastic environment to work in - supportive, challenging, fun and hugely rewarding to coach a large number of ambitious English players.
"Winning the Amlin Challenge Cup and the Aviva Premiership in successive seasons has given everyone involved with the club a boost, but we recognise that these successes are only a start."
Gilbert has released a new line of rugby cleats. The Gilbert Virtuo 8S is part of the exciting new product. Check it out.
The Barbarians are one of the top invitational rugby sides with a long history and classic rugby jersey.
The Nike Tiempo is a solid rugby cleat and one of few styles still made from full-grain natural leather.
The Lions get ready for their matches with this green training jersey. It's what the players wear. Get in the Gear!
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.
$29.99
The Lions are ready to get their Australia tour underway. They arrive in Perth on Monday.
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.
