His father's will stipulated that his mother, Princess Catharina Belgica of Nassau, should be the sole regent and guardian, and the Imperial Supreme Court confirmed this.

Count Philipp Moritz's rule began with an altercation between himself and his mother, Princess Catharina Belgica, about the termination of the regency and nature and the size of her widow seat.

They took their case to the Imperial Supreme Court and treated each other rudely; Philipp Moritz even removed his mother from the countly palace in Hanau.

When the Imperial troops reached Hanau, Philipp Moritz chose their side, in order to retain the military command of his capital.

He gave Philipp Moritz's brothers, Heinrich Ludwig (1609–1632) and Jakob Johann (1612–1636) the town and district of Steinheim, which was also a former possession of Mainz.

Hans Jakob Christoffel von Grimmelshausen used the occupation of Hanau by the Swedish as background in his picaresque novel Simplicius Simplicissimus.

From September 1635 to June 1636, Hanau was unsuccessfully besieged by imperial troops under General Guillaume de Lamboy.

2 February] 1638, Johann Winter von Güldenborn, a major in the Hanau army, supported by members of the Wetterau Association of Imperial Counts, staged a coup against the Swedes.

Philipp Moritz died on 3 August 1638 and was buried in the family crypt his father had established in the Church of St. Mary in Hanau.