[1] His terms of office, occurring during the reign of Emperor Justinian I, were marked by controversies with both imperial and papal authority.

[2] Eutychius' career is well documented: a full biography, composed by his chaplain Eustathius of Constantinople, was preserved intact.

The subscription of Eutychius to the Acts of this synod, which was later recognized as the Second Council of Constantinople and which concluded on 2 June 553, is a summary of the decrees against the Three Chapters.

[5] However, Eutychius came into violent collision with Justinian I in 564, when the Emperor adopted the tenets of the Aphthartodocetae, a sect of Non-Chalcedonians who believed that Christ's body on earth was incorruptible ('aphthorá) and subject to no pain.

[3] Upon the death of John Scholasticus, whom Justinian I had put in the patriarchal chair, the people of Constantinople demanded the return of Eutychius.

[3] Contemporary reports claim that as he entered the city, a large group of people met him, shouting aloud, "Blessed is he that cometh in the name of the Lord," and "Glory to God in the highest, on earth peace".

[3] In imitation of the entrance of Jesus into Jerusalem (recorded in Matthew 21:1–11 and John 12:12–18), he entered the city on an ass's colt, over garments spread on the ground, the crowd carrying palms, dancing, and singing.

[3] Toward the end of his life, Eutychius maintained an opinion that after the resurrection the body will be "more subtle than air" and no longer a tangible thing.

Some of his friends later told Pope Gregory I that a few minutes before his death he touched the skin of his hand and said, "I confess that in this flesh we shall rise again"[8] (a rough quote of Job 19:26).