The 21-year-old had another 12 months left on his contract with the Tigers but is keen to secure regular football after making just four Super League appearances this year.
"I am really happy to have the chance to come and play for Featherstone," he said. "I had another year remaining on my contract at Castleford but I need regular game-time in order to further progress and this is a great fit for me.
"I think coming to a club like Featherstone will benefit me a great deal, as a player and a person. It is a fantastic club and I can feel something special happening here.
"The Championship is getting more and more competitive every year and with a team coming down, Toronto Wolfpack coming in and a number of teams strengthening their squads, it is going to be even tougher in 2018."
Rovers coach John Duffy said: "Bringing Tom to Featherstone represents a major coup for us and we are delighted to have got the deal across the line.
"Tom is undoubtedly one of the most exciting young talents in the game and he has a massive future ahead of him."
Happy to say I've officially signed for @FevRovers for next season.— Connor Farrell (@confarrell93) September 8, 2017
Here's to finishing the super 8s well and kicking on next year 🔵⚪️
Castleford coach Daryl Powell said: "This is a great opportunity for Tom to play regular rugby league in the Championship.
"Tom has been developing within our system for a few years now and has played a number of first-team games where he has acquitted himself really well. However, we feel now is the right time for him to focus on playing weekly in the Championship environment."
Featherstone have also completed the signing of Wigan second rower Connor Farrell, younger brother of England international Liam Farrell, following his loan spell.