Rovers manager Les Parry said: "Marvin is a very promising young striker and I'm delighted to have signed him on loan.
"We've been short of goals recently and hopefully Marvin will bring us some added firepower. He's fast and strong and will be a good addition to our squad.
"I'd like to thank Watford manager Malky Mackay for allowing Marvin to come on loan to us."
Sordell will be available for Tranmere's home game against Oldham on Saturday.