Lee, 25, has been an ever present for the City Knights in 2014, scoring 18 tries in 19 appearances, as the two sides battle it out for a place in next year’s re-formed Championship.
Hawks Director of Rugby, Darren Williams, said: “We were alerted to Jack’s availability and moved swiftly to secure his services on a two year deal. Myself and head coach Barry Eaton have been aware of Jack’s talent and his consistency since he joined the Knights in 2010 from Featherstone Rovers and he will be a key recruit for 2015 and beyond.
“Talks are currently taking place with a couple of potential recruits to strengthen the squad before the window closes and for the upcoming play off series.”
Lee’s current club, York, sit top of the table with 45 points, ahead of Oldham on 42, and Hunslet on 39, although the Hawks do have a game in hand.