In 1966, the Nigerian crisis came to a head. Okigbo, living in Ibadan at the time, relocated to eastern Nigeria to await the outcome of the turn of events which culminated in the secession of the eastern provinces as independent Biafra on 30 May 1967. Living in Enugu, he worked together with Achebe to establish a new publishing house, Citadel Press.
With the secession of Biafra, Okigbo immediately joined the new state's military as a volunteer, field-commissioned major. An accomplished soldier, he was killed in action during a major push by Nigerian troops against Nsukka, the university town where he found his voice as a poet, and which he vowed to defend with his life.[12]