Moloney met with a host of Lions' medical staff including their doctor and physiotherapist, while touring the club's training facilities.
The 28-year-old is a restricted free agent, but Melbourne elected not to match the Lions' offer.
After being used in just 15 games in 2012, the 2011 Demons best and fairest winner said he was excited about joining the Lions.
"Brisbane's a proud club with a good culture and I'm really looking forward to the opportunity," Moloney said immediately before taking his medical.
"I just thought it was the right fit for me. They won 10 games last year, just outside the finals, and I'm looking to play finals footy and I think they've got a good young list."
Moloney - who has just returned from an overseas holiday - said a chat with Lions coach Michael Voss on Monday helped make his decision.
The clearance specialist appears a perfect fit for the team that finished 13th last season but struggled around the stoppages.
Veteran Simon Black, now 33, and youngster Jack Redden were the two most consistent midfielders in the clearances.
With 145 games to his credit (23 for Geelong and 122 for Melbourne), Moloney said after looking up to Voss his entire career, he was looking forward to being coached by him.
He said the time was right to move from Melbourne.
"It was [tough to leave]," he said.
"I barracked for Melbourne my whole life but I thought it was the right move for me and it was time for a fresh start."
Michael Whiting covers Brisbane Lions news for AFL.com.au. Follow him on Twitter: @AFL_mikewhiting
