Philip IV and his older half-brother Albert of Nassau-Weilburg were educated in the Protestant faith by Kasper Goltwurm at Neuweilburg Castle.

As Philip was only sixteen years old, John III of Nassau-Saarbrücken, the senior member of the Walram line of the House of Nassau took up the guardianship.

He participated in the preparation of the Dutch War of Independence against Fernando Álvarez de Toledo, 3rd Duke of Alba.

In 1570 John III of Nassau-Saarbrücken wrote a last will and testament, appointing the half-brothers Albert and Philip as his heirs.

John had no male offspring and wanted to ensure that the counties of Saarbrücken, Saarland and Ottweiler were preserved by the Walram line of the House of Nassau in accordance with the inheritance treaty of 1491.

Their ancestor Adolf of Nassau, the only member of the family to be elected King of Germany, had been temporarily buried there.

In 1572, Philip had Wanborn Castle, a 12th-century structure in the vicinity of Saarbrücken, torn down and a Renaissance style hunting lodge with four wings named Philippsborn constructed on the spot.

John III died in 1574 and the Catholic counties of Saarbrücken, Saarland and Ottweiler fell to Albert and Philip of the Weilburg branch of the House of Nassau.

Duke Charles III of Lorraine, demanded the county Saarwerden back as a completed fief.

Catholic priests were converted to the new faith or removed from office; church property was confiscated; schools were established and patronage was acquired.

They had only child: After the Erika's death in 1581, Philip married on 3 October 1583 Elisabeth of Nassau-Dillenburg, a daughter of John VI "the elder" of Dillenburg.