Lilley made his Rhinos debut in 2015 and has played 41 games for his hometown club, but despite signing a three-year contract 12 months ago - has featured only four times this year.
The 21-year-old had a 12-game loan stint at Bradford last season and has had spells this term as a dual-registration player for Featherstone Rovers and on loan at Leigh Centurions.
His Rhinos deal will have a year to run when the loan arrangement expires next autumn.
Bulls coach John Kear said: “This signing is a further statement of intent from the Bulls in adding quality players to an already strong squad.
“I look forward to working with Jordan and harnessing his ability, skills and enthusiasm for the good of the team.”
Bradford chairman Andrew Chalmers added: “Jordan is an extremely talented player and he really gelled with the team last year.
“He’s going to play a crucial role in the side for the rest of the year as we enter the race to achieve promotion.”
Lilley - who is coach of National Conference Division Two leaders Stanningley - is available for Bulls’ first versus second Betfred League One showdown with York City Knights on Sunday.