Little is known of his life; except that he was condemned for heresy at the Council of Aquileia (in the northeast of modern Italy) in 381.
Palladius of Ratiaria (province of Dacia, modern Bulgaria) had been assured by Gratian, the senior Roman emperor, that several bishops from the Eastern Empire, a stronghold of Arianism, would attend the Council.
From the Council, Ambrose wrote to Gratian: No heretical bishops were found to be present except Palladius and Secundianus, men long notorious for their perfidy, on whose account people from the ends of the Roman world were asking that a council should be convened.
[...] We are horrified, most gracious princes,[Note 2] at sacrilege so terrible and teachers so depraved; and to prevent their peoples being any further deceived, we came to the conclusion that they ought to be deposed from their priesthood[.]
[...] We beg you, out of regard for your own faith and honour, to show respect for the Author of your empire, and, by the letter of your Grace to the competent authorities, to decree that these champions of impiety be debarred from the threshold of the Church, and that holy bishops be put in the place of the condemned by the representatives of our humble selves.