The 20-year-old has only recently returned from a loan spell at Carlisle and will link-up with Yeovil as they battle against relegation from the Championship.
Murphy netted three goals in 11 appearances for Carlisle and Glovers boss Gary Johnson has welcomed his arrival at Huish Park.
"I am very pleased to be able to bring Tom into our squad from Manchester United. He's a player that can play either side wide or as a regular number 10," he told the club's website.
"Tom has got tremendous potential and has shown that at League One level with Carlisle and Manchester United have given us the opportunity to bring him on further in the Championship."
Teenage defender Joey Jones is heading out of Somerset after being loaned to Skrill Premier side Woking for one month.