After starting in every game this year for the Sea Eagles, he signed a deal on Tuesday until the end of 2019.
The 29-year-old, lured back to rugby league last year from Rugby Sevens, has flourished under coach Trent Barrett in 2017 to be a cornerstone of their pack.
"I am very grateful for the opportunity Trent gave me last year after three years out of the game," Winterstein said.
"For me, it was about making the most of the opportunity and I have loved every moment of it.
"When the offer came to re-sign with the Sea Eagles for a further two years, I couldn't turn it down."
Barrett added: "Frank took a punt with us and we took a punt with him. He is a pleasure to coach and his teammates love him in the side."
Photo: Copyright: NRL Photos. Sea Eagles back-rower Frank Winterstein (right) has re-signed with the Sea Eagles.