Reardon is currently awaiting sentencing after pleading guilty to assault, but has moved to the KC Stadium after becoming a free agent despite still having a year left on his contract.
Hull FC Head Coach, Richard Agar, said: “Stuart will give us some much needed depth and cover to our back line and I know he is looking forward to joining up with the squad.”
Reardon said: “Hull FC is a massive club and one which has challenged for major honours over the last few seasons. I can’t wait to join up with the squad and hopefully contribute to their push for further honours.
“My recent court case has been well documented, whilst my actions were very much out of character I acknowledge that does not justify or excuse my behaviour which I deeply regret.
“I am hoping that moving to Hull will give me a new start and I intend to be a positive influence in the club not only as a player but also off the field supporting their numerous community focused initiatives.”