She first appeared as Mon Mothma in the prequel film "Star Wars: Episode III - Revenge of the Sith" (2005), although her role was very brief.
Later, she reprised the role in the series "Star Wars Rebels" (2014-2018) and in the series "Andor" (2022-present), where she has a much more prominent role.
It's worth noting that a different actress, Caroline Blakiston, played Mon Mothma in the original trilogy films, but Genevieve O'Reilly is considered the definitive portrayal of the character in the current continuity.