In 300 or 301 he attended the provincial Synod of Elvira[8] (his name appearing second in the list of those present), and upheld its severe canons concerning such points of discipline as questions concerning clerical marriage, and the treatment of those who had abjured their faith during the recent persecutions.

[9] The Council appears to have had Novatianist tendencies and held a strict view that refused readmission to those baptized Christians who had denied their faith or performed the formalities of a ritual sacrifice to the pagan gods under pressures of persecution.

[10] In 313 he appears at the court of Constantine the Great, mentioned by name in a constitution directed by the emperor to Caecilianus of Carthage in that year.

In his new role as patriarch, Eusebius and his supporters brought pressure to bear upon Constantius II to expel Athanasius of Alexandria, a staunch anti-Arian, for a second time from his diocese.

[8] Continued pressure from Eusebius led to Constantius' writing a letter demanding whether Hosius alone was going to remain obstinate in his support of Athanasius.

From his exile he wrote to Constantius II his only extant composition, a letter justly characterized by the French historian Louis-Sébastien Le Nain de Tillemont as displaying gravity, dignity, gentleness, wisdom, generosity and in fact all the qualities of a great soul and a great bishop.