The 23-year-old French Guiana-born prop forward, who is the first South American to play in Super League, has become a crowd favourite since joining Castleford from Catalans Dragons halfway through the 2015 season on a two-and-a-half-year deal.
Tigers coach Daryl Powell said: "Gadwin has worked exceptionally hard since he has been at the club to develop all aspects of his game.
"He is a big physical specimen whose ball carries are a real threat to opposition defence. I have no doubt he will continue to improve and develop into an all-round outstanding front rower of the future and I'm delighted that he has agreed to extend his contract at the club."
Springer said: "I feel very happy to be staying at Castleford for two more years. Since I have come here I have improved a lot and I think of Cas as my second home now.
"I think it is great that the fans chant for me and I appreciate how they support the team. I just love playing at Jungle! We have a great side and I hope we can win something soon. I think that if we go through the season with no injuries we can achieve something great here at the Tigers."