The 20-year-old has penned a five-year deal at St. James' Park.
"I am so happy to have signed for Newcastle," Mitrovic told the club's official website.
"I visited the stadium and it is amazing. I have played in a lot of impressive stadiums in my career but St. James' Park is so big, I can't wait to play my first game here.
"I know how passionate the fans are. This is a club with a very big history and the fans are a big part of that. There will be pressure here, for sure, but I like pressure.