The 21-year-old impressed for Blackburn last season and has become a key player at Ewood Park.
The new deal will keep Nzonzi at Blackburn until the summer of 2015.
“We are delighted to secure Steven for the long term,” Blackburn chairman John Williams told the club’s official website.
“He was outstanding last year – his first in this country – and the new deal is richly deserved. We hope he makes further progress and continues the fantastic form that impressed so many people last season.
“Along with the new contracts also agreed with the likes of Phil Jones, Martin Olsson and Grant Hanley, and the important re-contracting of Morten Gamst Pedersen, this represents further good progress for the club this summer.
“However, there is still business to be done. We remain determined to secure a new striker and I can assure all our supporters that our search continues in earnest in that regard.”
