Pellaeon saw action in his youth during the Clone Wars for the Galactic Republic. He would continue to serve after the Galactic Republic became the Galactic Empire under Palpatine's regime. After Palpatine's death and the fragmentation of the Empire, Pellaeon served as captain aboard Grand Admiral Thrawn's flagship, the Chimaera, acting as Thrawn's personal assistant and enforced the Admiral's will aboard the ship, giving his own opinions on occasion, until the Admiral's death. Pellaeon would later rise in the ranks of the Imperial Remnant, becoming a Grand Admiral himself and striking peace treaties with the New Republic, working out of the Remnant's new capitol base on Bastion. He retired to his home on Bastion, but was forced back into service as Chief of State during the Second Galactic Civil War in 40 ABY by Jacen Solo, aka Darth Caedus, on behalf of the Galactic Alliance in an effort to attack the planet Fondor. Because he did not trust Jacen, he secretly enlisted aide from his old ally, Natasi Daala.
As the battle went on, the people of Fondor surrendered. However, Jacen ordered that the attack continue, making an example of the people of Fondor. Pellaeon ordered that they cease fire, but was approached by Tahiri Veila, Jacen's apprentice and pawn, who threatened him with death should he defy Solo's orders. Pellaeon ordered his fleet to turn on Jacen, which resulted in the other Moffs taking control of the Imperial Fleet and joining Solo and Pellaeon's death at Tahiri's hands - but not before Pellaeon sent off a message to Daala, who joined the battle. With the help of her Mandalorian allies led by Boba Fett, she took control of Pellaeon's ship, the Bloodfin, and defeated Caedus' fleet in the battle.
Later, Daala would take control of the Galactic Alliance herself.
After his death
Pellaeon's name would live on not only in his legendary acts, but also in the Pellaeon-class Star Destroyer used by the Fel Empire almost a hundred years after his death.