Shortly after his election, he was made a member of the legation sent by Pope Hormisdas to the court of the Emperor Justin I in Constantinople, the purpose of which was to negotiate an end to the Acacian schism between the western and eastern churches.
The contemporary Liber pontificalis refers to him as "Capuan bishop" (Capuanus episcopus) in connection with this legation and provides a terminus ante quem for his assumption of episcopal office.
In a letter to Justin's nephew, Count Justinian, Pope Hormisdas specifies that the members of his legation were selected for their "quality".
On Thursday, they met with the emperor, Senate and patriarch all at once in the Palace to present the libellus Hormisdae, the document entrusted to them by the pope outlining his conditions for the healing of the schism.
[1] The Liber pontificalis credits Germanus with deftly handling the Theopaschite controversy, the calculation of the date of Easter and the reintegration of bishops deposed by the Emperor Anastasius I.
[1] According to the tenth-century Chronicon Salernitanum, Germanus changed the dedication of the Constantinian basilica of Capua from the Apostles to Saints Stephen and Agatha after depositing there some of their relics that he had obtained as a reward from the emperor himself.
[1] Pope Gregory the Great in his Dialogues mentions how Benedict, praying atop Monte Cassino, had a vision of the soul of Germanus in the form of a ball of fire being carried to heaven by angels.
In his Dialogues, Gregory the Great prays to Germanus to intercede on behalf of the soul of a deacon named Paschasius in Purgatory.
In late 873, following a campaign against the Arabs harassing Capua, the Emperor Louis II of Italy took some of Germanus's relics to Monte Cassino, according to the Chronica monasterii Casinensis.
Since the Vita sancti Germani episcopi Capuani (Life of Saint Germanus) mentions neither of these transfers, it was probably finished before 873.