Sergios 12 was known as Antipisides; he was a deacon, known as a calligrapher (τὸν διάκονον Σέργιον ... τὸν λεγόμενον Ἀντιπισίδην, ἐπειδὴ καλῶς καλλιγραφεῖ) in the time of the patriarch Paul II of Constantinople (Paulos 2) (641-653), when he was shown how to write Latin characters by the Latin grammatikos Konstantinos 24 and made a fair copy of the latter's translation of the libelli of Vigilius, on the instructions of Paulos 2; he then delivered the copy to Konstantinos 24; during the fourteenth session of the Third Council of Constantinople (5 April 681) he gave evidence about his part in the affair; he was still a deacon of the Great Church (Hagia Sophia) (διάκονος τῆς ἁγιωτάτης τοῦ Θεοῦ μεγάλης ἐκκλησίας): Riedinger II 2. 652-654 (= Mansi XI 596). He was therefore a deacon from at least 653 to 681.

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