Tansey, 22, has earned rave reviews in the NRL for his performances at full back and hooker for the Roosters, will move to the KC Stadium in 2010, cutting short his protracted two year deal Down Under.
He said: “I have really enjoyed the experience of playing for the Roosters and I’m totally committed to giving them my best throughout the rest of this season.
“However, when Hull came in for me it was an opportunity I felt I couldn’t turn down.”
“I am excited by the signing of Fitzgibbon, who I know well from my time here and obviously the recent signing of Sean Long is massive for the club and I can’t wait to play with him.
“My chats with Richard Agar went really well and I loved the sound of what he wants to achieve and I am desperate to play my part in that.
“Joining Hull also allows me to be closer to my friends and family again which is very important to me and I can’t wait to run out in front of the Black and White fans at the KC.”
Hull are paying a £30,000 transfer fee to Leeds to secure the transfer, as Tansey was under contract at Headingley until 2011.
“He gives us versatility,” said Hull coach Richard Agar. “We are looking to make our attack a little more potent and Jordan fits that bill.
“He can play right across the back line; he is quick, skilful and kicks well. Anyone who saw him at Leeds knows he can come off the bench and have an impact and can certainly change games.”