The 23-year-old impressed with the bat in 2021, scoring 842 runs across all formats and recording his maiden first-class century against Sussex in the LV= County Championship in May.
Zaib played in all bar one of Northants' matches in all competitions, and head coach John Sadler is delighted the player has committed to the club, particularly after his efforts in 2021.
“It’s fantastic that Saif has extended his stay with us,” said Sadler.
“He's a multi-format cricketer who has really improved this season in all aspects of his game so the club were keen to get him locked in early.”
Zaib, who hails from High Wycombe, has been with Northants since he was a teenager and made his first team debut as a 15-year-old back in 2014.
An excellent fielder and accomplished left-arm spinner, Zaib has always been viewed as an all-rounder, but he was used last summer primarily as a batsman, only bowling 67 overs in all competitions across the season.
With the bat, he averaged 27.42 in the Championship, scoring 576 runs in 22 innings, 26.4 in the Royal London One Day Cup and just shy of 20 in the Vitality T20 Blast.