The Emergency Powers Act represented a change to the Galactic Constitution. It was enacted at the very beginning of the Separatist Crisis during the year 24 BBY. Its purpose was to permit Sheev Palpatine to continue serving as Supreme Chancellor well beyond the conclusion of his originally mandated terms. The legislation was envisioned to be active only for the duration of the Separatist Crisis.
On the day before the First Battle of Geonosis occurred in 22 BBY, Junior Representative Jar Jar Binks successfully persuaded the Senate to broaden the authority granted to the Chancellor under the emergency powers. This was motivated by the perceived danger posed by the Confederacy of Independent Systems. This expansion allowed Palpatine to circumvent the Military Creation Act and establish the Grand Army of the Republic. Palpatine used the expanded Emergency Powers Act to maintain his position as Chancellor throughout the Clone Wars.
Throughout the Clone Wars, the Constitution was modified four more times through additional amendments, which further increased the scope of Palpatine's emergency powers. As a result, Palpatine attained a level of power exceeding that of any chancellor since the time before the Ruusan Reformations. One such modification was the Reflex Amendment, which vested the Chancellor with almost unlimited authority over military matters, essentially bypassing the Senate's oversight. The Senate was unaware that Palpatine was secretly Darth Sidious, a Sith Lord, who had deliberately orchestrated the Clone Wars to ensure his continued tenure and to facilitate the destruction of the Jedi Order. The passage of the Emergency Powers Act was, in a sense, a step towards Sidious' larger plan to overthrow the Galactic Republic and replace it with the Galactic Empire.
During the restoration of the Galactic Republic, which took the form of the New Republic, Chancellor Mon Mothma was given the same emergency powers that had previously been granted to Supreme Chancellor Sheev Palpatine through the Emergency Powers Act. However, Mothma's intention was to eliminate these powers because of the harm they caused to democracy.