The midfielder will be joining the Reds squad in USA for the pre-season tour. He has been presented the number 5 jersey at Liverpool.
Georginio Wijnaldum scored 11 goals last season for Newcatsle in 38 appearances. The Magpies were relegated from the Premier League.
Liverpool confirmed the league on twitter. The twitter read:
After joining the club, the player said: "I'm really excited because Liverpool is a big club with a great history and it's always a dream to play for as big a club as Liverpool."
When the player was asked about the prospect of working with Jurgen Klopp, he added: "A great man - from the outside - because I don't know how he works yet and I have to work with him.
"I always love to watch him, his passion as a trainer, I like how he enjoys the game. He gives something back to the group, so I look forward to working with him."
Liverpool manager Jurgen Klopp too sounded excited after roping in the Dutchman. He said: "I am so happy that we have got him and he can join us now in the USA.
"I think he can be a great player for us. He has already shown some really good moments in his career but the most exciting and important thing for me and my staff is that there is still so much extra to come from him.
"When I talked to him I could tell that he knows we have to work together to get this level out of him.
"He has played a lot for his country already, been captain at a young age in Holland, and also been involved in a tough Premier League season, so this experience gives him a good foundation for the challenge here - which everybody knows is huge!
"He can play a few positions for us and players that come through the Dutch system usually have a good tactical understanding and flexibility. That's really important.
"I can't wait to get him on the training pitch and for the fans to see him play in a Liverpool shirt."
Georginio Wijnaldum becomes the Reds' seventh signing this season. They have already signed Loris Karius, Joel Matip, Marko Grujic, Sadio Mane, Ragnar Klavan and Alex Manninger.