Frederick was in the Polish army, where he reached the rank of Lieutenant-General and participated in many battles against the Ottoman Empire.

[citation needed] After Frederick's death in 1698, his widow and Ferdinand became guardians of the minor heir, Friedrich Wilhelm Kettler, and ruled the duchy in his name.

When Friedrich Wilhelm died, he left Ferdinand as the last heir to the throne of Courland from the House of Kettler.

However, in 1736, the King of Poland, August III, in a private meeting, offered the throne of Courland to Ernst Johann von Biron.

A month later, the Council of the Duchy elected Ernst Johann von Biron as the new Duke of Courland and Semigallia.