The 22-year-old put pen to paper on a six-year deal with United, keeping the frontman at St. James' Park until the summer of 2025.
Joelinton will wear the famous number nine shirt and could be in line to make his United debut in Saturday's pre-season friendly at Preston North End.
Joelinton told nufc.co.uk: "I'm really happy to be here. I know the club is investing a lot in me and it's a huge responsibility. But I'm happy, motivated and I hope to give something back on the pitch.
"I know it's a big club, with massive history here in England and around the world. I've followed the Premier League from Brazil since I was little and know about the huge tradition of the club and how passionate the fans are.
"I'm passionate about the game. I bring a lot of emotion on to the pitch. I'll never being lacking in desire and dedication. I like playing football and like to enjoy myself on the pitch.
"I hope to have a great career here. As I said before I'm really happy and hope to bring a lot of joy to the fans and everybody involved with the football club."