The midfielder signed a contract until 30 June 2031 and will wear the number 25 shirt.
Onyedika enjoyed a successful four-year spell in Belgium, winning two league titles, the Belgian Cup and Supercup.
On the international scene, he has earned 26 caps for Nigeria and featured in their 2024 Africa Cup of Nations squad. .
“Raphael Onyedika has not only impressed us with his physicality and strategic understanding of the game, but above all with his extraordinary consistency,” said board member for sport Markus Krosche.
“He has been a regular starter in recent years and has won numerous trophies in Belgium. He also boasts valuable international experience.
“At 25, he still has great potential and is an important building block in terms of the structure of our squad.”