Orford, the 2008 Dally M winner, will join former Sea Eagles 2008 premiership winners Steve Menzies, Glenn Hall and Heath L'Estrange at the English club.
In a club statement, Orford says there's nothing "sinister" about his switch and he has always wanted to finish his career in England.
"This opportunity came earlier than expected but the chance to play with good friends at a club which is on the rise accelerated my decision.
"There is nothing sinister in the switch. I could have remained with Manly for two more years but decided the time is right now.
"I have loved my time with the club since I returned from Melbourne Storm."
It leaves coach Des Hasler without a recognised halfback for 2010, although Kiwi utility Keiran Foran is likely to be seen as a suitable replacement, pairing Jamie Lyon in the halves.