Cartwright will join the the South Sydney Rabbitohs, who he signed a three-year deal with from 2021.
The 23-year old departs his Penrith contract four months early early after no first-grade appearances this season.
Cartwright made his NRL debut in Round 17 last year in his only game for the club.
Panthers general manager Matt Cameron thanked the backrower for his contributions to the club.
“Jed has been offered an opportunity to play NRL for his new club this season and given the circumstances it would be remiss of us to stand in his way,” Cameron told penrithpanthers.com.au.
“We thank Jed for his service to Panthers and wish him the best of luck with his future endeavours.”
Cartwright's arrival to Redfern has been fast tracked. ✈️ Welcome to the family Jed! 🐇❤️💚
— South Sydney Rabbitohs 🐰 (@SSFCRABBITOHS) July 30, 2020