The highly-rated teenager joined City's Academy at the age of nine and won the Under-18s Premier League title in 2022/23, before continuing that form last season with eight goals and four assists to his name before arriving at St. James' Park.
On joining the 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."