The 24-year-old arrives from Chelsea on loan until the end of the season, with an option for the Magpies to make the move permanent next summer.
Atsu began his career at Portuguese giants Porto and spent time on loan at Rio Ave before Chelsea snapped him up in the summer of 2013.
In three seasons at Stamford Bridge, the winger has enjoyed loans at Vitesse, Everton, Bournemouth and Malaga – scoring four goals in 24 appearances for the latter in the second half of last term.
Atsu has won 44 caps for Ghana since making his international debut in June 2012. He represented his country at the 2014 World Cup, and also helped the Black Stars to the final of the 2015 Africa Cup of Nations, being named Player of the Tournament and scoring the goal of the tournament.
“I’m very happy to be at Newcastle,” said Atsu.
“It’s a very big club. They have good facilities and I think Newcastle have one of the best coaches in the world.
“St. James’ Park is a fantastic stadium with 50,000 fans; the fans here really love football so much and I can’t wait to play at this stadium in front of the fans.”
Newcastle United manager Rafa Benitez said: “I agreed with our fans that we needed to bring in another winger, so I am very happy to welcome Christian to the Club.
“He has good ability and pace in the wide areas and also has good experience of English football.
“He has a different style of play to the other players we have at the moment and that will be important for the squad.”