The Galactic Republic was the name of the galactic government prior to the establishment of the Galactic Empire in 19 BBY. Although it was commonly known as the Old Republic, this was not so until the establishment of the Empire; its name when it existed was the Galactic Republic, or simply the Republic. Rarely, it was referred to as the First Republic. At times, the term Old Order was used to describe it.

The Republic, led by a Supreme Chancellor, had a supposedly democratic government that was able to sustain itself for over twenty-five thousand years. It is said that its complete history would "fill a thousand libraries".

In its latest years, it was a benevolent—though ineffectual—government tied up in layers of bureaucracy.

The Republic was born with the signing of the Galactic Constitution c. 25,000 BBY, during the Unification Wars. During that time, the Humans and Duros, reverse-engineering the Force-based technologies of the Rakata, invented the hyperdrive, allowing Coruscant to become the capital of the Galactic Republic and would remain that way for twenty-five thousand years. The Republic was created by the Core Founders.

Shortly after the formation of the Republic, the Perlemian Trade Route was mapped, linking Coruscant to Ossus, and bringing the Jedi Knights into the Republic. Over the next millennia, the Corellian Run was mapped, linking Coruscant to Corellia and beyond. The wedge defined by the two trade routes became known as "the Slice." Since the stretch of hyperspace galactic-west of Coruscant was anomaly-ridden and impassible for current Republic technology to traverse, the government expanded eastward, instead. The Core Worlds' portion of the Slice was known as the Arrowhead, and soon the Republic expanded into the Colonies.