The 22-year-old graduated through the academy system at Franklin's Gardens and has gone on to make 86 appearances since his debut against Esher in 2007.
Lawes has won the European Challenge Cup and LV= Cup in his time at the club, while he was in the side that suffered the agony of losing to Leinster in the Heineken Cup final.
And the 13-time capped England international claims he had no hesitation in committing his long-term future to the club.
"It means a lot to sign a new contract with the Saints because I've grown up around here," Lawes said. "It's good to sign on again and see myself with a future at the club. I enjoy playing here and working with the coaches and want to stay here for as long as I can.
"I think I've improved a lot as a player in recent years, which has all come from playing here and being coached here. The coaches keep us grounded off the field and I've still got a lot to learn from them on the field.
"Winning the LV= Cup and European Challenge Cup are obvious highlights, as was playing in the Heineken Cup final - even though we lost. Playing in front of a packed Franklin's Gardens is really good, too. The fans are great here and really get behind us."
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