In 1547, during the Schmalkaldic War, he conquered the Castle and Lordship of Delmenhorst, which had been lost to Münster in 1482.

The Order of St. John sued him about their stolen possessions; after a lengthy trial, Anthony prevailed.

With the assistance of farmers from Stadland and Butjadingen, which his father had conquered in 1514, he managed to gain a large amount of fertile territory by constructing levees around some wetlands in the Jade Bight.

In 1566, his brother Christopher died, and Anthony became the sole ruler of Oldenburg and Delmenhorst.

Anthony married on 1 January 1537 in Oldenburg, to Duchess Sophie of Saxe-Lauenburg (d. 7 October 1571 in Oevelgönne), the daughter of Duke Magnus I and Catherine of Brunswick-Wolfenbüttel.