Mallinder, who captained the England side that won the 2016 Junior World Cup, has become a regular in the first team under director of rugby and father Jim Mallinder this season.
With his future at Saints now secured, Mallinder is looking forward to continuing his development at Franklin's Gardens.
"The Saints is my only club and I never considered going anywhere else," he told the club website. "I've grown up at Franklin's Gardens and experienced some great memories already, both as a player and a young supporter of the club.
"Looking at the environment and the squad we have building here, I'm extremely positive about what is to come over the next few years."
Meanwhile, Saints hooker Dylan Hartley is free to play in the autumn internationals for England against Argentina, Australia and Samoa after disciplinary action against him was dismissed.
The front-rower was cited for striking Clermont Auvergne's Rabah Slimani in the European Champions Cup loss to Clermont Auvergne, but a disciplinary panel has not taken any further action against the Northampton talisman.