Ferdinand has made just three appearances for Posh this season and spent November on loan at League Two side Northampton.
The 21-year-old will be available for the Hatters' match against Lincoln on Saturday.
"He's an all-action midfield player who plays a high-energy game," Luton boss John Still told the club's official website.
"He can come up with the odd goal and for him to play 30-odd games in the Championship last season speaks volumes.
"It's all happened a bit quick but he'll travel with us to Lincoln and, all things being equal, he'll be in the squad."
Ferdinand started his career at Southend and, after two seasons with the Shrimpers, was signed by Peterborough for £200,000 in August 2012.