The Premier League club secured the 20-year-old on a five-year contract from Belgium's Anderlecht, according to a statement from Newcastle. The club did not comment on the fee, which would make Mitrovic one of the most expensive players in the club's history.
Mitrovic came through Partizan Belgrade's youth system before he was bought by Anderlecht for 5 million euros two years ago.
He scored 44 goals in 90 matches for Anderlecht and has been capped 13 times for Serbia since June 2013, scoring one goal.
