The 23-year-old joins Eddie Howe’s side for a reported fee of £55 million following an impressive season at Nottingham Forest.
Elanga enjoyed the most prolific campaign of his short career in 2024-25, scoring six goals and providing 12 assists in his 43 games across all competitions.
He will now feature in the Champions League for Newcastle after the edged-out Nuno Espirito Santo’s high-flying side towards the end of the season.
Speaking to the club’s in-house media team, Elanga said: "I'm excited, I'm really happy but most importantly I'm ready. I'm ready to put on this black and white top to really fight for this team and give everything for the passionate fanbase that lives and breathes football.
"I had an amazing two years at Nottingham Forest, they really helped me to become the player I am today, but I'm really happy to be here now. The club won a trophy last season and are building something unique, something special that I really want to be part of.
"I really want to buy into the culture, into the DNA of this club. I'm really happy to be here and I can't wait to get started."