The New Republic Fourth Fleet constituted a significant fleet element within the New Republic Defense Fleet. It is believed to have evolved from the Rebel Alliance Fourth Battle Group. Under the successive leadership of Voon Massa and Chel Dorat, the fleet participated extensively in the New Republic liberation campaign during the two years following the Battle of Endor. Beginning in 8 ABY, it transitioned into a major defensive force stationed in Bothan Space, and it engaged in the last major fleet campaign of the Galactic Civil War against the Imperial Remnant in 17 ABY.
In 28 ABY, the Fourth Fleet, along with the rest of the Combined Defense Forces of the New Republic, underwent reorganization, emerging as the Galactic Alliance Fourth Fleet.
Following the Battle of Endor, the Fourth Fleet was placed under the command of Admiral Voon Massa and operated from Bothan Space, tasked with liberating the Corellian Run. The fleet achieved victories at Druckenwell, Milagro, Spirana, and ultimately captured Denon. Although Massa perished at Denon, the victory enabled the New Republic to advance into the Colonies. Chel Dorat succeeded Voon Massa as Admiral.
During the Thrawn campaign, the Fourth Fleet served as a rapid response force stationed at Bothawui. During the 12 ABY restructuring of the New Republic Defense Fleet, the Fourth Fleet was reorganized around a modular structure of task forces and battle groups.
During the Black Fleet Crisis, the Fourth Fleet was withheld from the New Republic's operations in the Koornacht Cluster. Near the conflict's conclusion, it was deployed to blockade Nanta-Ri.
Admiral Dif Scaur held the position of commander of the Fourth Fleet before his appointment as Director of New Republic Intelligence. Garm Bel Iblis commanded it in the 17 ABY campaign against Daala's replacement warlords in the Deep Core, achieving victory at the Battle of Columus.
It later transitioned to become the Galactic Alliance Fourth Fleet.