Bienek, 23, first came to prominence as an explosive teenage forward with the Broncos, earning him a move into Super League with Hull FC in 2018.
The strong-running front-row spent three years with the Airlie Birds but struggled to make his mark and joined Castleford ahead of this season on a one-year contract.
With his former Hull boss Lee Radford having taken over at Wheldon Road for 2022, Bienek has been allowed to move on once more.
The Ireland international - who hails from Sidcup - returns to Broncos in the Championship and and head coach Jermaine Coleman said: “Lewis is an exciting talent.
"Coming through the ranks you could tell he was going to be special but unfortunately it hasn’t quite worked out for Lewis at Hull and Cas.
"However, he is still a very special player. After speaking with Lewis it was clear he wanted to come back to his roots and be a part of what we are trying to create this year.
"He will have a huge impact for us this season and is desperate to see the club be successful.”
“I’m looking forward to being back home in London," added Bienek.
"It’s where it started for me and means a lot to be back. I’ve gained a lot from my time at other teams that I want to take into 2022.
“Having spoken with Jermaine about his goals for the team I feel I can bring something to the table and cannot wait for pre-season to start.”