His mother was the granddaughter of the Paramount Ruler Chief Chukwuani (died 1930) from Ozalla, Nkanu West Local Government Area, Enugu State, Nigeria.

He earned his Bachelor of Divinity degree in sacred theology from the Urban University in Rome in 1987,[3] and was ordained to the priesthood on August 8, 1987.

[3][4] On February 9, 2009, Onaga was appointed by Pope Benedict XVI as the Enugu diocesan bishop after the resignation of Anthony Okonkwo Gbuji.

[8] Later that same day, Onaga appointed Monsignor Luke Adike as the diocesan Vicar General, and Very Rev.

[12] Onaga was the guest speaker for the Igbo Catholic Community USA (ICCUSA) Eighth Annual Convention between April 23 and 25, 2010,[13] held in Sacramento, California.