The 20-year-old Irishman, who has made his first-team breakthrough this season, has committed himself to the club until the summer of 2013.
Devitt said: "I'm delighted. I've been playing games and I just want to keep playing games for Hull City. Everybody wants to be playing and that is what you train all week for.
"If you're not playing, it can be frustrating, but that's when you just have to get on with things and hope the manager puts you in for the next game."
Devitt made his first senior appearance for Hull on the opening day of this season against Swansea and has made seven starts since.