The 27-year-old, whose contract had been due to expire next summer, has played 152 times for the Premiership side since his debut in 2009.
He was part of the Lions squad in New Zealand this summer, appearing in five warm-up matches on the tour.
"I strongly believe we have a squad capable of going places and I'm really excited for the season," Marler said.
Marler, who came through the Quins academy, is a former club captain and helped them win the 2012 Premiership title.
He has been part of the England team which has claimed back-to-back Six Nations crowns, including the Grand Slam last year.
"Joe is now established as one of the best loose-head props in world rugby," added Quins director of rugby John Kingston.
"He has displayed a real commitment to the Harlequins cause over many years and as an academy protege, he is another member of the squad who has only ever known one club."
England and British and Irish Lions prop Joe Marler has signed a new deal to stay at Harlequins until 2021.