The experienced central midfielder has joined the Roosters from fellow Turkish Super Lig side Trabzonspor.
Onazi signed a one-and-a-half year contract with Denizlispor and the club has an option for another year.
“WELCOME ONAZI! Our club signed a 1.5-year contract with Nigerian player Ogenyi Eddy Onazi, with one-year option,” a club statement read.
Onazi spent four years with Trabzonspor as one of the key players until he started struggling with injuries in 2018.
The 27-year-old player will be hoping to help Denizlispor retain their status in the top-flight league this season.
The Roosters were promoted to the Super Lig at the end of the 2018/19 season after winning the TFF First League.
They are currently placed 11th on the 18-team league standings ahead of the second round.