The 33-year-old all-rounder helped the Steelbacks win the T20 Blast competition in August, and has spent two seasons with the side.
In that time he has taken 81 County Championship wickets and scored 782 runs, with 30 wickets in T20 cricket.
"Rory Kleinveldt is a Steelback to the core, we love having him here," said Northants head coach David Ripley.
Former South Africa international Rory Kleinveldt has signed a new one-year contract with Northants.