Caretaker-boss John Carver, who worked with the teenager during his time as coach at Newcastle, said: "I've seen a lot of him at Middlesbrough and followed his progress as a player.
"He's made a few senior appearances, so he's got some experience. He's a young lad, a left-sided player and I'm looking forward to working with him again."
Johnson has made just four first-team appearances for ‘Boro this season.