The 35-year-old, who has been one of the Broncos' most influential players throughout a torrid season, had led the side since joining in 2012.
Tony Clubb, the 25-year-old England international centre or second-rower, has been appointed as his successor.
Gower, a dual-code international having also represented Italy in rugby union, will remain a member of the squad and is contracted until the end of 2014.
The Broncos are bottom of Super League after winning just three of their first 16 games, and coach Tony Rea hopes the change will spark an upturn in fortunes.
Rea said: "Tony has all the attributes of a leader - he's been in the system for eight years, leads from the front and is a proud Londoner.
"He has other attributes the team can look to in the heat of battle.
"It certainly gives us an opportunity to share the leadership around.
"Craig, as a playmaker, will always show the intensity to play the game hard and work hard - the change just enables us to have another dimension to the leadership."