Doubts were raised over the 32-year-old's future in recent months but Evans, who is also known to play at fullback, has quashed any suggestions of leaving by agreeing to an extended stay, according to Sky Sports News.
"Myself and my family are happy to have the opportunity to stay at Harlequins," Evans told the club's official website. "I'm looking forward to continuing to play with a great bunch of lads and to working with a special coaching staff.
"There is no limit to what this team can achieve and I am excited to have an influence both on and off the field. My decision was made easy by the ambition of this great club, the success we have had and the hunger to want more."
Director of rugby Conor O'Shea added: "There is not a player, supporter or coach in the game in England, let alone Harlequins, who will not be delighted that Nick Evans has agreed to stay with us for another three years."
Evans has been playing for the Quins since 2008.