Donatos 2 was bishop of Ostia; in 866, when the bishop of Rome, Nicholas I (Nikolaos 28), sent envoys to Bulgaria to convert the people to Christianity (see Paulos 57 and Formosus 1), he also sent Donatos 2 ("Donatum episcopum Ostiensem") with the priest Leo 164 and the deacon Marinos 15 to accompany them to Bulgaria and then to continue onwards to Constantinople to deliver there the judgments of pope Nicholas concerning the church of Constantinople (in the matter of the patriarchs Photios 1 and Ignatios 1); on the borders of Bulgaria and the Byzantine empire they were prevented from proceeding further by the local official, Theodoros 181, and were insulted and abused; they remained waiting for forty days, until they learned that the emperor forbade them entry into the empire and they therefore returned to Rome to report what had happened: Lib. Pont. 107. 70-72.

A Western bishop; in 868/869 he was one of the representatives sent by pope Hadrian II (Hadrianos 8) to attend the Council summoned at Constantinople by Basil I (Basilios 7) and the patriarch Ignatios 1; his colleagues were Stephanos 89 and Marinos 15 (Στέφανος μὲν καὶ Δονᾶτος ἐπίσκοποι τοῦ πάπα Ῥώμης, καὶ Μαρῖνος εἷς τῶν ἕπτα διακόνων σὺν αὐτοῖς): Nicetas, Vita Ignatii 544C.

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