Anthonius was born in the castle of Ten Walle in Beveren in 1576, son of Philip Triest, knight, lord of Auweghem, and Marie van Royen.

From 25 November 1617 to 28 January 1618 he was absent from his diocese on a mission to reconcile the Duke of Lorraine and his brother, the Count of Vaudement.

As bishop he supported charitable institutions such as the newly established mount of piety (that provided interest-free credit to the poor) and an orphanage for girls, re-organised Sunday schools, encouraged the foundation of confraternities and patronised the arts.

His intelligent interest in the visual arts gained him the friendship of Peter Paul Rubens, Anthony van Dyck and David Teniers the Younger.

He was summoned to Rome to answer before the Pope, but on 29 August 1652 the Council of Brabant issued an order under the jus de non evocando forbidding him from pleading his case before a foreign tribunal.