Sharp, 24, has been one of Quins’ stand out performers since going full time in 2007 and moves north with the option for a third-year.
The centre or wing man said: “I didn’t want the opportunity to pass and wonder what if and I really want to test myself at Hull. When a club like Hull comes along with the potential to be a top three team it is hard to ignore.
“That is no disrespect to Harlequins where I have really enjoyed myself, but this is a new challenge, a chance for me to show what I can do, score some tries and hopefully earn a spot in the England squad.”
Sharp, who was born in Nigeria, was brought up in Bradford and started his rugby league career with Queensland Amateur club at the age of just seven, before eventually joining the Harlequins academy.
Hull coach Richard Agar said: “We are delighted we have secured the services of Will from 2011. He is a talented, young and ambitious player and we are pleased he thinks that Hull FC is the place to realise those ambitions.”
Sharp was Quins’ young player of the year in 2008 and has scored six tries this season for the struggling London club.