Matt Moylan, 25, extended his deal by four years, while Bryce Cartwright re-signed for another three.
After taking over as Panthers captain, Moylan made his State of Origin debut this year for New South Wales.
He has played 71 NRL games and scored 18 tries since making his debut for the club in 2013.
Cartwright, a veteran of 55 games, was similarly delighted to re-sign with the Panthers.
The Panthers reached the semi-finals this season, losing to the Canberra Raiders 22-12 on Saturday.