The highly-rated teenager joined City's Academy at the age of nine and won the Under-18s Premier League title in 2022/23 and continued that form last season with eight goals and four assists to his name before arriving at St. James' Park.
Harrison registered five goals across all competitions for United's under-21s side during the 2024/25 season as well as recording the joint-most assists in the Premier League 2 (7).
On joining Newcastle's Academy, Harrison said: "The size of the club and what it has got going for it is massive for me. It's got a huge, passionate fanbase and I'm looking to really push on with my career now.
"If I was a kid now, looking at me signing for Newcastle United, it's what dreams are made of. I'm really looking forward to what is coming and how I can progress in the coming years.
"I'm an effective player who can add goals and assists. I really like to create stuff but, on the other side, I'd also say I'm a very passionate player who always wants to win."