The 18-year-old has put pen-to-paper on a four-year-deal at Elland Road, running until the summer of 2026.
The central midfielder moved to the Etihad Stadium after catching the eye for Millwall's Academy back in 2018.
Speaking after the move was confirmed, Gyabi told LUTV about why he wanted to join the club.
He said: “I am really excited! Obviously I have seen that they've given the young players a lot of opportunities in the first team here.
“I think it was nine debuts in the Premier League last season, so that's really good! I know a bit about the club, it's a great club.
“The fans are what has attracted me the most. I played here last season and the fans were crazy in an Under-23s game!
“So, I can't imagine how that's going to be in a full stadium."
Gyabi was asked about what the fans can expect to see from him as a player, when he pulls on the white shirt.
“I like to get on the ball," he explained.
“I like to drive with the ball and carry the ball, I am creative and I like to score goals as well, I can keep possession and play forward.
“Off the ball I am very aggressive and I can press, I work hard as well. I want to push and help as much as I can with the team, get into the squad and show what I am about."