The 13-goal top scorer, who was linked with Fulham and Wolves last month, has committed himself to the club until the summer of 2013.
"I'm really pleased to sign the deal," he told the club's official website.
"I'm looking forward to playing my part in the future success of Millwall."
Morison, 27, joined from Stevenage for ?130,000 in July 2009 and has hit 36 goals as well as earning his first call-up to the Wales squad.
Source: PA
Source: PA