Adamson, 26, played 135 games for Salford after making his debut in 2006, and then switched codes in October 2012, playing rugby union for Bath, making a solitary first team appearance against Newport Gwent Dragons.
He has spent the past two seasons with Championship side Halifax, making close to 50 appearances.
He said: “I’m extremely excited about joining the Broncos for 2015 and heading back into a full time environment again.
“I’ll be moving down away from my family and my sole focus will be rugby next year and getting the promotion back in to Super League and with the squad that’s being put together that’s a real expectation.”
Broncos head coach Joey Grima added: “Luke will bring a good deal of Championship and Super League experience to the side next season having previously played for Halifax in the Championship and Salford in the Super League.
“We’re very close to finalising our squad for the 2015 season. Our retained players along with some invited academy players are training up until the beginning of October before we all take a break and return for pre-season training at the beginning of November, we’re in a great position with our recruitment and we are deep in planning for pre-season.”