The 19-year-old has been handed the number nine shirt at Gigg Lane.
Cullen progressed through the youth ranks at the KC Stadium after being released by Newcastle aged 15.
After scoring 33 goals from 30 youth and reserve team games during 2009/10, Cullen made his senior debut for the Tigers against Sunderland before further appearances against Wigan and Liverpool.
Cullen made 21 appearances for the Tigers last season, scoring once in the Carling Cup tie against Brentford in August.
Cullen had a one-month loan spell at Bradford last season.