The young winger’s move from Galway United was confirmed after impressing during a trial last summer.
Now an Ireland youth international, Fitzgerald hopes to follow in the footsteps of fellow Galway native Alex Murphy by breaking into the first team.
"I'm very happy," the 18-year-old told the club's website.
"I had a few conversations with different clubs but as soon as Newcastle came in, it was a no-brainer for me.
"I was on trial in the summer and I really liked the city, people and the atmosphere at St. James' Park. I want to play for fans who really enjoy hard work, goals and creative players.
"The project really attracted me. Steve Harper and Paul Midgley (head of youth recruitment) showed me the pathway of players such as Alex Murphy, who came through Galway's academy and then signed for Newcastle like myself.
"I used to go to the same school as Alex but I was two or three years younger than him. I did look up to him because he was in Galway's first team when I was at the academy. Hopefully, I can follow in similar footsteps."
Academy director Steve Harper added: "We are delighted Kyle has chosen to join the club amidst lots of interest from other big clubs.
"He has impressed during a trial period with the academy and we are very pleased he is joining us at this crucial stage of his career.
"Our talent pathway has had some big success stories in recent years so the challenge is there for Kyle and all of our players to continue their development and hopefully follow in the footsteps of those who have gone on to compete in the first-team squad."