The midfielder, 28, has been training with his former club and has impressed boss Tommy Wright enough to earn a short-term contract.
The former Manchester City player had a spell on loan with the Perth side in 2012 while registered to Derby County, before moving to Oldham.
Croft had been without a club since the summer before sealing his return to McDiarmid Park.
Wright told the club's website: "I know what we are getting with Lee.
"He did well for us the season before last and I am confident he has plenty to offer us this season.
"He played 54 times last season for Oldham and I'm surprised he has found himself in this position but I'm delighted to get him for the remainder of this season and maybe even beyond."