Sanderson, 27, joined on a two-year deal in February and helped Northants win the T20 Blast, taking 3-31 as they beat Durham Jets in the final.
"I'm delighted to have signed a new three year deal. I'm looking forward to playing with these boys for more years to come," he told the club's website.
"He is a very skilful bowler and very popular member of the squad," head coach David Ripley said.
Northants bowler Ben Sanderson has signed a three-year deal with the club.