He was the fourth son of John I, Marquis of Namur, and Mary of Artois.
When his older brother Guy was killed in a tournament in Flanders in March 1336, Philip became his successor.
From there he traveled to the Holy Land via Cyprus, with his brother-in-law Henry II of Vianden.
It is recorded that "Philippus comes Namucensis" (as he was called) donated property to St Alban, in accordance with the testament of "frater noster dominus Guido quondam comes Namucensis", by charter dated 23 Jun 1336.
Philip and the Count of Vianden were buried in the Franciscan church of Famagusta.