Hardaker has been on loan from Leeds Rhinos since the start of this season. Rhinos will receive a £150,000 transfer fee for the former Man of Steel, who was a member of their treble-winning squad two years ago,
Hardaker scored 67 tries in 155 games for Leeds before joining NRL side Penrith Panthers on loan 12 months ago.
He moved to Tigers, on long-term loan, in the closed season and was one of their try scorers in last Friday’s 23-12 win over Rhinos at Headingley which took Cas seven points clear at the top of Super League.
“I am really thankful for the opportunity [coach] Daryl Powell and [chief executive] Steve Gill gave me to come to Castleford at the start of the season,” Hardaker said.
“To get the chance to stay here, I just jumped at the offer. I have fully enjoyed my time here so far and I think we have a couple of exciting years ahead of us. It was an easy decision to stay here once I got the offer.
“The fans are amazing. It’s quite a close-knit community and the fans are so loyal. It’s great for myself to be around the club and I really enjoy playing for the people of Cas.”
Powell was in charge at Featherstone Rovers when Hardaker joined them from amateur club Featherstone Lions in 2010.
“Signing Zak is a huge deal for the club,” Powell said.
“For quality players and indeed international players to come to Castleford and then want to stay and commit their long-term futures here, I feel says a lot about us as a club.
“Zak is continuing to improve as a player and I believe he will continue to do so over the coming seasons.
“I look forward to working with Zak and helping him to firstly to do something special with Castleford and then grow as an international player and play in the World Cup at the end of the season.”
Gill added: “We are all thrilled at Castleford Tigers to be able to bring a quality player like Zak into our squad.
“His form this year has put him back in the England set up and he has been a great replacement following Luke Dorn’s retirement. I would like to thank (chief executive) Gary Hetherington at Leeds Rhinos for the integrity and honesty he has shown throughout the course of these negotiations.”