Muscat joins Millwall
The Australian international has agreed a three-year deal with Lions boss Mark McGhee after Rangers agreed to release the player on a free transfer.
"The timing of the move is brilliant," Muscat told the club's website. "A lot has happened in the last three days and I'm just grateful to be here.
"I played under the gaffer at Wolves and I'm more than happy to sign for him again."
Muscat failed to establish himself in the first team at Rangers and the Scottish champions were keen to get the full back off their wage bill.
"I've decided it's in my best interests to be playing regular football," stated the 30-year old.
"I enjoyed my time at Rangers but I think this is the right move for me just now."
He added: "I've spoken to several people, and I heard nothing but good things about the club so I had no hesitation in coming."