[1] Theodotus was born in Nakoleia,[1] as the son of the patrician Michael Melissenos by the sister of Eudokia, the last wife of Emperor Constantine V. Theodotus had become attached to the court bureaucracy and was a confidant of Emperor Michael I Rangabe.

By the time Michael I Rangabe was deposed by Leo V the Armenian in 813, Theodotus I was an elderly spatharokandidatos, whom the near-contemporary Scriptor Incertus describes as "meek" and "uneducated".

[1] On 14 March 815, Leo V forced the resignation of Patriarch Nicephorus I of Constantinople, and appointed the pro-iconoclast Theodotus Melissenos in his place.

In the aftermath of this synod Theodotus I is representing as torturing by starvation at more than one iconodule abbot in an attempt to force them into agreement with his ecclesiastical policy.

He ceases to be mentioned in the sources after the murder of Leo V and accession of Michael II in December 820.