Fleet Group Three was one of the three primary fleets serving within the New Republic Defense Force during the time of the Battle of Coruscant. Under the command of General Wedge Antilles, who directed operations from the Star Destroyer named Mon Mothma, its role was to act as the hammer in a strategic maneuver, complementing the anvil formed by Fleet Groups One and Two. This fleet experienced the fewest casualties during the battle because General Antilles hesitated to engage refugee vessels that the Yuuzhan Vong fleet was forcing to crash into Coruscant's planetary shield. This resulted in thousands of his ships deserting to Garm Bel Iblis's Fleet Group Two, a consequence of their commander's reluctance to attack.
Following the order to retreat from Coruscant, a leading element of Fleet Group Three executed a hyperspace jump to Borleias and successfully drove out the Yuuzhan Vong occupation force, thereby reclaiming the planet for the New Republic. Antilles intended to establish this world as a temporary refuge for the countless refugees fleeing the galactic capital; however, the self-proclaimed Chief of State Pwoe and the remaining members of the Advisory Council pursued the fleet to Borleias and instructed General Antilles to remain on the planet indefinitely to harass the Vong forces. Pwoe's true motive was to have Antilles and his fleet sacrifice themselves, allowing him time to prepare for a formal surrender to the Vong. Antilles recognized the Senator's deceitful plan and successfully blackmailed him into permitting the remaining elements of Fleet Group Three and the Star Dreadnought Lusankya to reinforce him at Borleias.
Despite the Lusankya's success in destroying one of the Yuuzhan Vong battle groups dispatched to suppress the Republic presence on Borleias, it and Fleet Group Three endured a months-long siege by an even larger force commanded by Commander Czulkang Lah, the father of the current Warmaster, Tsavong. The Battle of Borleias concluded with Fleet Group Three's complete withdrawal, but only after they had destroyed Czulkang Lah's worldship and the majority of the Vong fleet. Subsequently, the fleet underwent reorganization due to losses, merging with the Third Battle Group and adopting the new designation of Third Fleet as a component of the newly established Galactic Alliance Defense Force.