In the last years of the Galactic Republic, Mon Mothma represented Chandrila in the Senate. Though a Loyalist Senator, Mothma worried about Supreme Chancellor Palpatine’s accumulation of power and the militarization of the Republic.

Mothma allied herself with like-minded Senators such as Alderaan’s Bail Organa, Rodia’s Onaconda Farr and Naboo’s Padmé Amidala. But their efforts to curb Palpatine’s powers proved largely in vain.

In the final months of the Clone Wars, Mothma and Bail Organa laid the groundwork for resistance to Palpatine’s rule, fearing that he would refuse to give up the emergency powers granted during the fight against the Separatists. Palpatine ultimately declared himself Emperor, and Mothma remained in the Imperial Senate, but worked in secret with Organa and other operatives including Luthen Rael and her cousin, Vel Sartha, to unite rebel factions into an Alliance to Restore the Republic.

Unfortunately, Mothma had little support for her work from her colleagues and her immediate family. Her teenage daughter, Leida, preferred Chandrilan traditions to Coruscant politics. Her husband by arranged marriage, Perrin Fertha, enjoyed the amenities of being a senator’s spouse but did little else to support Mothma. When she became aware that she was being monitored by the Imperial Security Bureau, the pragmatic senator exploited Perrin’s past gambling troubles to throw the Empire off the trail of her efforts to fund the Rebellion, secretly working with her old friend Tay Kolma.

During Leida’s wedding to the son of Chandrilan banker Davo Sculdun, Mothma learned that her childhood friend Tay Kolma was now a security risk, as his secret support of Mothma’s rebel causes had led to a decrease in his personal wealth. Despite her political positions fracturing many of her personal relationships, Mothma pushed on, attempting to gather votes to block an attempt by Palpatine to tighten his iron grip over the Imperial Senate.

After the massacre on Ghorman, Mothma decided to go public with her opposition to Palpatine. While practicing her speech, she was approached by Luthen. He warned her that Bail Organa’s team, who were meant to help her escape the Senate building after she gave her speech, had been corrupted. During the next Senate session, Mothma called out the lies of a Ghorman insurrection her fellow senators were promoting, and named the massacre an Imperial genocide orchestrated by Emperor Palpatine. Mon Mothma became a public enemy of the Empire following her outspoken public condemnation. It was her final act as senator. Shortly after Cassian Andor helped her avoid Imperial arrest, the Ghost crew escorted Mothma to a secret location; there, she put out a call for other rebel cells to join her. A flurry of ships came to her signal, and the Rebel Alliance was born.

The need to strike out against the Empire became urgent when the Alliance, from their base on Yavin 4, learned of an Imperial superweapon. Mothma tasked Jyn Erso, daughter of Death Star weapons architect Galen Erso, to contact extremist rebel Saw Gerrera, as well as her father, in an effort to discover a weakness in the battle station. Ultimately, the leading council of the Rebellion would vote not to attempt a covert operation to secure the plans; Erso, with a small band of rebels, took matters into their own hands and went to Scarif, home of the Imperial data center that housed the Death Star schematics. When Mothma discovered this deception, she did not block it. Instead, she readied the rebel fleet to support Erso and receive the data transmission, resulting in the plans coming into the care of Princess Leia Organa.

In rapid succession, the Emperor disbanded the Senate and Mothma's ally, Bail Organa died when the Death Star destroyed Alderaan. Mothma went into hiding, serving as the political leader of the Rebel Alliance. But after waging a five-year Civil War to restore the democratic ideals, the Imperials were defeated and Mothma was elected Chancellor of the New Republic.