The 18-year-old midfielder joins the Heed after impressing on trial in recent weeks and most recently appeared against Hebburn Town on Friday, assisting JJ O’Donnell’s goal in the 4-2 win.
Greenfield is making his first step into senior football with the move, having been on the books with Manchester United up until under-13 level before joining Barnsley, who he helped finish sixth in the U18 Professional Development League North last season.
The midfielder revealed he can’t wait to get started on Tyneside, telling gateshead-fc.com: “It’s been a lot of hard work trying to show Mike and the coaching staff what I can do.
“I’m happy to join and hopefully he can trust me enough to put me in the team.
“It’s been a great experience playing with the first-team, the lads have been class with me since I’ve come in.
“To get on the pitch with them on Friday and show what I can do on the pitch was good, they helped me a lot as well.”
The teenager added that one of the main factors in making the move to the North-East was playing under the guidance of player-manager Mike Williamson.
“He’s a big reason why I came here,” Greenfield continued.
“He’s obviously played a number of games in the Premier League and he’s an experienced pro so I can learn a lot off him as a young lad.
“I’m looking to show Mike that I’m more than capable of playing in the team and hopefully help Gateshead get back to where we need to be.”