The MC90 Star Cruiser represented a warship class that the Mon Calamari designed specifically for the New Republic.

The MC90, which was produced at the Mon Calamari Shipyards, holds the distinction of being the first Mon Calamari Star Cruiser engineered from the ground up as a dedicated warship. Its emphasis on potent weaponry and sizable hangar bays demonstrated a practical understanding of the firepower necessary to effectively challenge Imperial-class Star Destroyers. Prior to the Yuuzhan Vong War, the MC90 stood as the most formidable warship constructed for the New Republic.
A notable advancement was the design of controls and displays on board, which, for the first time in a Mon Calamari Cruiser, were made compatible with a wide range of species. This allowed non-Mon Calamari officers to effectively pilot the vessels. The command center featured a transparent bubble at the ship's center, offering bridge officers a comprehensive view both above and below. Admiral Ackbar expressed his reservations about this design choice, arguing that it presented a vulnerable point that Imperial forces could potentially exploit.

The MC90's development commenced early in the New Republic's existence, with its plans receiving approval a mere six months following the Battle of Endor. However, due to the New Republic's limited resources at the time, the ambitious MC90 project faced delays to prioritize the development and production of the MC80B Star Cruiser.
The MC90 marked several significant milestones, underscoring the evolving military strategy of the New Republic, which would eventually culminate in the New Class program. The first MC90, named Defiance, was completed shortly before the Battle of Calamari.
The MC90 evolved into a premier warship within the New Republic Defense Fleet's arsenal, frequently serving as the flagship for fleets and task forces. Given the immense value attributed to these vessels, the majority were stationed within the Core Worlds.
These potent warships held their position as the pinnacle of Mon Calamari shipbuilding until the emergence of the Mediator-class battle cruiser. Older vessels, such as the Galactic Voyager, were maintained in reserve and underwent upgrades during the [Yuuzhan Vong War](/article/yuuzhan_vong_war], although their role was more symbolic than as heavy-duty combatants.

Despite the increasing prevalence of newer Mon Calamari-built warships within the Galactic Alliance Defense Force by 40 ABY, including the Mon Calamari heavy carrier and the Mediator-class battle cruiser, the MC90 continued to be regarded as a formidable frontline combat starship. This was exemplified by the Galactic Voyager's role as the flagship of Alliance Supreme Commander Cha Niathal.