The 24 year-old moves to St. James’s Park on a five-year deal to become the Magpies’ first signing under new head coach Steve McClaren.
The deal for Wijnaldum represents the third highest transfer fee in United’s history, after Michael Owen and Alan Shearer.
“I’m delighted to be a Newcastle United player,” said Wijnaldum.
“I felt the time was right for me to move and the club have shown they really want me, so I’m very happy to be here.
“There’s a few players here who are from Holland – I know them well and they will help me feel at home in Newcastle.
“I know the club has a great stadium with great fans. I want to play here as soon as possible – I want to feel the atmosphere and hear the crowd. I cannot wait to get started.”
Steve McClaren added: “This signing is a real statement for the club. It is a big transfer for a very good player and I am delighted to have Gini here at the club.
“He has lots of energy and a great tempo to his game. He is very skilful but is also capable of playing box-to-box, and – importantly – he can score goals.
“He is at the right age and the right fit for Newcastle. He is a leader as well and you will see that. He is someone who always wants the ball, can deal with it, and we need that kind of character in the team.”