The 25-year-old Belgian joined the club today.
The 24-year-old stopper arrives on a five-year deal in a move that comes as a surprise considering the needs of the Newcastle team currently.
The club have plenty of goalkeepers already but with Ron Elliot and Tim Krul both out with long-term injuries at the moment it seems that Newcastle boss Rafa Benitez decided another stopper was needed.
Newcastle manager Rafael Benitez
The Spaniard explained the decision to sign Sels to the official Newcastle United website:
"I am really pleased to welcome Matz to the club. He's a fantastic goalkeeper and many top clubs have been interested in signing him.
Newcastle United's Tim Krul
"Obviously we have injuries to Tim Krul and Rob Elliot which could be difficult for us in the first part of the season, so it was important to strengthen in this area to be sure we can make a strong start in the Championship."
Many Newcastle fans will however still be wondering why exactly the club are bringing in a goalkeeper when they are in dire need at other positions – left-back being a prime example.
Newcastle's Rob Elliot celebrates at the end of the match
But it seems that Benitez believes another goalkeeper was necessary to cover for the injuries and to take the pressure off of young Karl Darlow and Freddie Woodman when the season starts.
But with Krul stepping up his recuperation from injury it would certainly appear as though the Dutch international will have a major challenge getting back into the current Newcastle United set-up.