The Nigeria-born Singaporean forward has returned to Indonesia with the East Java club who have been in the search for a new striker
Based in Surabaya, East Java, home to Indonesia's most passionate supporters, the club confirmed Agu's transfer after a successful trial.
Persebaya coach Rahmad Darmawan also added that the forward will be club's last signing for the new season and will hopefully help to fill the problems in the goalscoring department.
"Yesterday we still lacked a pure striker, but with Agu Casmir joining the team, I think we have enough players," said Rahmad, whose team are currently competiting in the Inter Island Cup featuring teams from most of Indonesia's many islands.
"He will become our subtitute striker, or maybe become the right partner for Pacho (Emmanuel Kenmogne)."
Agu has been without a club since his departure from LionsXII at the end of the team's inaugural 2012 Malaysia Super League season. He has had prior playing experience in Indonesia having turned out for Persija Jakarta in 2011.
A naturalised Singaporean, the Nigeria-born Agu had also played for Gombak United, Woodlands Wellington and the Young Lions in the S.League, as well as Malaysian side PDPRM FA.