Onyedika, 25, arrives in a permanent deal reported at around €9m plus add-ons, with the Nigerian previously touted for a switch to Aston Villa and the Premier League before instead settling on a switch to the Bundesliga. He signs a contract running until the summer of 2031, becoming Frankfurt's fourth addition of the summer following the earlier arrival of Noel Aseko from Bayern Munich.
Primarily a holding midfielder but comfortable filling in at centre-back, Onyedika joined Club Brugge from Danish side Midtjylland in 2022 and made 183 appearances across all competitions during his four years in Belgium, helping the club win two Pro League titles, a Belgian Cup and a Super Cup, while also collecting six goals and five assists along the way.
Sporting director Markus Krosche said Onyedika's consistency had been just as impressive as his physical attributes.
"Raphael Onyedika has not only impressed us with his physicality and strategic understanding of the game, but above all with his extraordinary consistency," Krosche said.
"He has been a regular starter in recent years and has won several titles in Belgium.
"He also has valuable international experience. At the age of 25, he still has great potential and is an important building block in terms of the structure of our squad."
Onyedika missed Club Brugge's Belgian Super Cup defeat to Union Saint-Gilloise due to illness as the move edged closer, with Eintracht Frankfurt fending off a late show of interest from Saudi Arabian clubs to get the deal over the line.
The move marks Onyedika's first taste of German football and gives head coach Adi Hutter fresh options in central midfield as Frankfurt look to improve on an eighth-place finish in last season's Bundesliga.