Metropolitan bp. of Edessa, author, and translator. He was the older brother of Patr. Dionysios of Tel Maḥre and, like his brother, had been a monk at Qenneshre. His consecration as bp. took place under Patr. Quryaqos (d. 817) and was followed by some agitation among the Edessenians, which Quryaqos, however, was able to lay to rest (Michael Rabo, XII.7; Syr. 493; FT 3.28). Theodosios accompanied his brother on a trip to Egypt in 824/5. According to Barsoum, he died in 832.

Theodosios is the author of a historical work. This is not preserved, but it was referred to and used by his brother Dionysios, and through him it was known to Michael Rabo. In addition, Bar ʿEbroyo (Ecclesiastical History, ed. Abbeloos and Lamy, vol. 1, 361–64) attributes to him a Syriac translation of the poems (mušḥoto) of Gregory of Nazianzus. One poem, transmitted in ms. Vat. Syr. 96 (no. 20; S. E. and J. S. Assemani, Bibliothecae Apostolicae Vaticanae … Catalogus, I.2 [1758], 521) specifically attributes the translation to Theodosios, while he was priest in Edessa, and dates the translation to the year 802 (A. Gr. 1113, June to A. Gr. 1114, Dec.). This translation seems to be identical to the one preserved in ms. Vat. Syr. 105 (which was misdated by the Assemanis and belongs to the 9th cent.). Since these poems have been translated on three different occasions (see Gregory of Nazianzus), it is not always possible to distinguish between the work of each translator.