In youth Agu played at Rangers International, whose first team he aufrückte in January 1994. In the summer of the same year, the then 18 -year-old went to Bolivia and joined the Club Bolívar. He was also the first Nigerian who made it to the highest Bolivian league.
In 1995, Agu to Spain at that Erstdivisionär SD Compostela. However, in the following season 1995/96 he was only eight appearances for, among other things, because internationally experienced striker as Bent Christensen Arensøe and Ljuboslaw Penev were under contract at Compostela and because he himself had bad luck with injuries. In 1996 he moved to the second division CD Ourense.
From 1997, Agu played for eight years continuously in Germany, where he scored 2 goals in 18 second-division operations. His first stop there was the Oberliga Rathenow optics, in which the then unsigned striker initially only fithielt itself. When the A- team of the club but was threatened with relegation, Agu got a contract and scored 13 goals in just nine games, which helped the club to relegation.
Then he committed the second division Fortuna Cologne. But he could at the Fortuna, in which the competition by storm from Daniel Graf, Toralf Konetzke, the Congolese national team Macchambes Younga- Mouhani and the later German international Thomas Brdarić was, win a regular place. He came only seven times for input and also had problems with the coach Toni Schumacher.
Followed for Agu more stations in Germany, including the second division Wacker Burghausen who, however, was terminated after only one season after setting problems again. In addition, he was in the years from 1999 to 2005, four regional league under contract, by which the FC Schweinfurt was, where he helped with eleven goals in the 2000 /01 season for promotion to the second division. His most successful third league season had Agu VfR Aalen, for he 2001/ 02 in only 21 games hit 14 times. Together with his team mate Miguel Coulibaly and several other players, he finished in sixth place in the scorer in the Regionalliga Süd.
2005 Festus Agu returned to differences with the coach of FC St. Pauli from his home club Enugu Rangers back, where he ended his career.
- Promotion to the 2nd Bundesliga ( 1): 2001