She was born on planet Corulag. She served the Galactic Empire as an Imperial officer and pilot during the Great Jedi Purge. Her exceptional skills in leadership and combat were noticed by several high-ranking officials in the Imperial Military, including the Sith Lord Darth Vader. Rising through ranks in record time, Captain Eclipse was personally chosen by Vader to lead his Black Eight Squadron. Although she initially considered service under Emperor Palpatine's right-hand man to be the highlight of her career, her role in the Bombing of Callos caused her to doubt some of the Empire's policies. Although her beliefs wavered due to the mass genocide and complete sterilization that rendered Callos uninhabitable, Captain Eclipse was unwilling to abandon her allegiance to the Empire, nor her hard-earned position under Darth Vader's command. However, Vader came to the conclusion that Eclipse lacked a certain quality in ruthlessness that he found necessary in those who served him. As a consequence, he reassigned her to a highly confidential detail. Hence, in 3 BBY, Eclipse became the latest pilot of the Rogue Shadow, a stealth vessel that was piloted by several individuals in turn. The purpose of her top secret assignment was to transport Darth Vader's agent to wherever his missions required him to go. During that time, she was unaware that the mysterious young man was Vader's secret apprentice, codenamed "Starkiller."
Although she learned that Starkiller was a Force-sensitive assassin, who was tasked with hunting down the last of the Jedi, her attempts to learn any personal information about him were met with failure. Upon inadvertently discovering Vader's plot to kill Emperor Palpatine with Starkiller's aid, Eclipse's loyalties became divided between her Emperor and immediate superior. Nevertheless, she continued to carry out her orders to the letter, and took great care to not allow the apprentice to learn of her accidental discovery. But when Vader unexpectedly betrayed his disciple at the behest of the Emperor, the Dark Lord branded Captain Eclipse as a traitor due to her association with Starkiller. Stripped of her rank and all that she worked hard to gain, Eclipse was imprisoned on the Empirical.
Six months later, Juno Eclipse was freed by Starkiller, who's apparent death was faked by Darth Vader in order to continue their assassination plot against Palpatine. Eclipse, forced into the life of a fugitive, reluctantly renounced her allegiance to the Galactic Empire and joined with Starkiller on his mission to create the Rebel Alliance. However, she was unaware of the fact that the apprentice remained loyal to his master; nor did she realize that the Rebellion's purpose was to distract the Emperor's attention in order to create a new opportunity to kill him.
During their adventures, Eclipse and Starkiller gradually developed a rapport that eventually turned into love. When Vader betrayed the apprentice for a second time, Starkiller denounced the Sith and embraced his Jedi heritage. By that time, Eclipse learned that the apprentice's birth name was "Galen Marek." However, their relationship was brought to an untimely end when Marek perished in battle against Emperor Palpatine by sacrificing his own life in order to save the founders of the Rebel Alliance.
Shortly after Marek's death, Eclipse witnessed the official founding of the Alliance to Restore the Republic on Kashyyyk. She chose to honor the fallen apprentice's legacy by joining the Alliance Fleet as one of its first officers. Less than a year later, Juno Eclipse was commissioned as the captain of the Rebel flagship, the Salvation.