The 22-year-old Castleford-born player, who is a product of the Tigers' youth system, scored a 95-metre try to seal a 30-28 victory over Hull last Friday.
"It's a dream come true for me. I've been banging on (chief executive) Steve Gill's door for a while asking for a new contract," said Clare.
"I've got a hunger to keep playing for Cas and I want to repay the faith that has been shown in me by the coaching staff. It's still a surreal feeling for me that I am playing for Castleford Tigers."
Castleford coach Daryl Powell added: "I have been hugely impressed with James since I came to the Tigers.
"He has a quality temperament and a good skill set to go with it. His try last week showed just how quick he is and there will no doubt be many more moments like that for James at Castleford."
- Sports & Recreation
- Castleford Tigers