Genevieve O'Reilly, an Irish performer, took on the role of Mon Mothma in the motion picture Star Wars: Episode III Revenge of the Sith. She later reprised this role in Rogue One: A Star Wars Story, lent her voice to the character in five episodes of Star Wars Rebels, and appeared in two Disney+ television programs, namely Andor and Ahsoka.
On June 19, 2003, StarWars.com made the announcement that O'Reilly was selected to play Mon Mothma in Star Wars: Episode III Revenge of the Sith, a role previously held by Caroline Blakiston in Star Wars: Episode VI Return of the Jedi. During the initial selection process, she received a scene for her audition, and she made an effort to avoid overanalyzing how to pay homage to Blakiston. Chosen due to her close resemblance to Blakiston, she thoroughly examined the British actress's portrayal to accurately capture the character's vocal delivery and demeanor. O'Reilly shot several scenes intended to establish the groundwork for the formation of the Rebel Alliance. She found the experience of filming these scenes enjoyable and admired the exceptional quality of the costumes. Prior to the film's debut, director George Lucas and producer Rick McCallum communicated to O'Reilly that her dialogue-heavy scenes had been cut. The actress respected their choice, understanding that the film needed to prioritize the backstory of Darth Vader. Upon viewing the film, she fully understood the reason for the scenes' removal.
The revelation that O'Reilly would be returning as Mothma in the Anthology film Rogue One: A Star Wars Story came on April 7, 2016. She expressed her view that the film was an exceptionally stimulating and innovative undertaking. Furthermore, she provided the voice for her character in a number of episodes of the television program Star Wars Rebels, which was broadcast on March 4, 2017.
On April 24, 2020, a statement from StarWars.com confirmed that O'Reilly would be taking up the role of Mothma once again in the upcoming Disney+ series Andor. The actress expressed her delight at the chance to gain a more profound understanding of the character. She also conveyed her enthusiasm about delving into Mothma's roles as both a Rebel leader and a woman, which included revealing the private aspects of someone navigating a system characterized by oppression. O'Reilly aimed to grasp the suffering and personal sacrifices experienced by Caroline Blakiston in Return of the Jedi, and she relished the opportunity to learn more about Mothma's existence. She expressed her excitement for the audience to witness Mothma's transformation into the Rebel leader depicted in Rogue One. O'Reilly appreciated Tony Gilroy's writing style, noting that it incorporated numerous worlds and resonated as both universally relevant and deeply personal. The actress desired that Mothma's updated appearance in the show would reflect her evolved status as a prominent member of high society. O'Reilly believed that the scene featuring Mothma and Luthen Rael in the latter's gallery effectively established the objectives the team had for the character, which involved showcasing her public persona alongside the private individual within. The set's combination of public space and intimate interaction behind the corner fostered creative collaboration between O'Reilly and Stellan Skarsgård, the actor portraying Rael. O'Reilly enjoyed working with Skarsgård, considering him to be an exceptionally talented actor. The scenes set in the Chandrilan Embassy were filmed on a meticulously constructed set that incorporated a wraparound LED screen utilizing StageCraft technology. In September, 2022, O'Reilly was present at the Andor premiere event held in Hollywood, California.