On 19 August 1945 he was ordained deacon by Paul (Dmitrovsky), Archbishop of Tallinn and all Estonia; and later, on 8 February 1948 - priest by Isidore, Bishop of Tallinn and all Estonia. He was appointed rector of St Mary Magdalena Church in Haapsalu. In 1951 he graduated from the Leningrad (now S. Petersburg) Seminary (by correspondence).
In 1951-1957 he belonged to the clergy of Vologda diocese. On 27 February 1957 he was arrested by KGB and charged for "anti-Soviet agitation" (possession of religious books, conversations with believers). On 16 May 1957 he was sentenced to 10 years imprisonment (para 58-10 part I of the Criminal Code of Russian Federation), served his sentence in the political camps of Mordovia (Dubravlag). On 12 September 1960 the Supreme Court reduced the sentence to 5 years. On 7 September 1960 by the resolution of the Supreme Court of Mordovia he was released from custody ahead of time and put on probation. (He was rehabilitated on 14 October 1988). In November 1960 he came back to Estonia and became rector of John the Forerunner Church in Tallinn.
On 20 July 1990 at the first meeting of the Holy Synod, chaired by His Holiness Patriarch Alexy II of Moscow and all Russia, he was appointed Bishop of Tallinn, vicar to His Holiness Patriarch. On 21 August 1990 he took monastic vows in the Monastery of the Dormition at Pechery near Pskov and obtained the name of Cornelius; on 6 September 1990 he was elevated to the rank of archimandrite.
On 15 September 1990 he was ordained bishop at the Cathedral of St. Alexander Nevsky in Tallinn. The chirotony was done by Alexy, Patriarch of Moscow and all Russia, Tikhon, Metropolitan of Helsingfors (Finnish Orthodox Church), Evgeny, bishop of Tambov and Michurinsk, Victor, bishop of Podolsk and Lev, bishop of Novgorod and Staraya Russa. Upon the decision of the Holy Synod to grant autonomy to Estonian Orthodox Church he became the head of Estonian Orthodox Church with the title of Bishop of Tallinn and all Estonia. In 1995 he was elevated to the rank of archbishop.
On 6 November 2000 he became Metropolitan of Tallinn and all Estonia.