Until 1932, he taught in the Faculty of Orthodox Theology at Warsaw University, but was dismissed under political pressure from Polish nationalist elements.

On 9 October 1940 Ohienko accepted a tonsure of monk in Jabłeczna Orthodox monastery by Metropolitan Dionysius (Waledyński), taking the name Ilarion.

His cheirotonia was carried by Metropolitan Dionysius (Waledyński), Archbishop of Prague Savvatij (Vrabec) and Bishop of Lublin Timothy (Szretter).

Throughout his long career, in addition to church work, Ohienko contributed to scholarship and other areas of Ukrainian culture.

He was a populist committed to bringing the church closer to the common people, spreading the achievements of scholarship among wider circles of the public, and narrowing the gap between the literary language and the vernacular.