Bryan, 24, was released by the Broncos earlier this month, and makes the move in to the Championship.
He has made 33 appearances for the capital club, and has also spent time on a dual-registration deal with London Skolars.
The Jamaican international said: “I’m really looking forward to joining Featherstone Rovers. I know Featherstone is only a small town but I know it’s got a lot of heart.
“I’ve heard lots of positive things about Daryl Powell and he has done a terrific job so far at the club. I’m hoping that I can contribute to an already very good team and look forward to meeting my new teammates.”
German-born, Bryan started his rugby league career at South London Storm, before making his way through the Broncos academy.
He has played in a number of positions in his career, including wing, centre and second row.
Head Coach Daryl Powell said “Lamont is a dynamic back rower who I believe will become a firm favourite at Featherstone Rovers. His ability to break tackles is excellent and I believe he will complement our current back rowers very well. I look forward to working with him over the next two years as we constantly seek to improve our standards.”