The Jailbreak took place on the penal colony of Ord Vaxal in the year 20 BBY. It all started when a group of inmates in a medium-security prison overpowered their guards and seized control. The news of their triumph rapidly spread across the entire planet, leading to widespread revolts in the other correctional facilities. Within a couple of weeks, vast armies of escaped convicts had managed to reach the spaceports of the planet. In response to this crisis, the Republic deployed its naval forces to lay siege to Ord Vaxal. Given that the prisoners had established such a strong presence on the planet's surface, the Republic's strategy was to prevent them from escaping. The spaceports of Ord Vaxal were subjected to intense orbital bombardment, effectively trapping the massive number of prisoners on the planet. This was followed by a period of feudal-style conflict, as certain prisoners established small territories centered around the former prison complexes. The situation eventually stabilized into a fragile peace, although the Republic continued to maintain a rotating picket fleet in orbit.
Sometime after the situation on the surface reached a state of equilibrium, Palpatine made the decision to utilize Ord Vaxal as a dumping ground for political opponents, rebels, and various other criminals. Throughout the Imperial Era, individuals who had been condemned would be unceremoniously dropped onto Ord Vaxal, with no concern for what might happen to them on the planet's surface.
The first mention of the Jailbreak appeared in the article titled Ord Vaxal: Prison Planet of the Empire, which was featured in issue #165 of the roleplaying game magazine Polyhedron in 2003. The article was authored by Gary Astlefords. The article indicates that the Jailbreak occurred two decades prior to the Rebellion era, which commences in 0 BBY. However, it also states that Palpatine "came to power" after the Republic's naval forces had already established a presence in orbit around Ord Vaxal. Palpatine was elected to the position of Supreme Chancellor in 32 BBY and created the Grand Army of the Republic in 22 BBY. It is possible, though, that the reference is to Palpatine's transformation of the Republic into the Galactic Empire in 19 BBY.