During the Imperial Era, the Steadfast functioned as an Imperial I-class Star Destroyer within the ranks of the Imperial Navy. In 6 BBY, Enric Pryde, an Imperial officer, received orders to report to the ship. The commander of the Star Destroyer, Commodore Freylon, met his death at the Battle of Ponolapo by 0 BBY. Subsequently, Scaanos took Freylon's place as commodore, thereby becoming Pryde's commanding officer.
In 4 ABY, during the Battle of Endor, Pryde held the rank of captain on the ship until Scaanos instructed him to participate in the ground invasion of the moon. Later, during the Battle of Jakku in 5 ABY, Pryde was in command of the Steadfast when it met its end. Following the destruction of the vessel, he deserted his post and escaped to the Unknown Regions.
Being an Imperial I-class Star Destroyer, the Steadfast's length was measured at 1,600 meters.
The Steadfast began its service in the Imperial Navy during the Imperial Era after its commissioning in 6 BBY. After excelling at the Alsakan Academy and within five years of completing his training as an Imperial officer, Enric Pryde was assigned to the vessel in 6 BBY. When Commodore Freylon was serving as commander of the Star Destroyer, he was killed during the Battle of Ponolapo by 0 BBY. That same year, Commodore Scaanos succeeded Freylon, also becoming Pryde's superior officer.
Sometime between 3 ABY and 4 ABY, Pryde, then a lieutenant commander, was temporarily reassigned to the Star Destroyer Impervious for an inspection mission to Zee-Nine City Seven within Hutt Space. By 4 ABY, Pryde had returned to service on the Steadfast. During the Battle of Endor of 4 ABY, he served as the ship's captain against the Rebel Alliance. During that engagement, Scaanos ordered him to leave the ship and join the ground forces fighting the rebels on the Forest Moon of Endor's surface, while the Imperials engaged the Alliance's fleet in space. The battle concluded with an Imperial defeat.
Pryde later was in command of the ship during the Battle of Jakku in 5 ABY, where the Galactic Empire was at war with the New Republic, the successor to the Rebel Alliance. During this conflict, the Steadfast was shot down and destroyed, after which Pryde abandoned the Star Destroyer and escaped to the Unknown Regions; the Empire surrendered after its loss in the battle. Pryde assisted in the establishment of the First Order, the Empire's continuation, and advanced through its ranks. Snoke, the Supreme Leader of the First Order, eventually gave him command of a Resurgent-class Star Destroyer in 28 ABY, naming the command ship Steadfast to honor Pryde's former Star Destroyer.
Enric Pryde was assigned to the Steadfast in 6 BBY, remaining there for his entire Imperial career and becoming the crewmember with the longest tenure by the Battle of Endor in 4 ABY. He later took command of the ship during the Battle of Jakku in 5 ABY. Commodore Freylon was the ship's commander until he died at the Battle of Ponolapo by 0 BBY, at which point Commodore Scaanos replaced him that year, also becoming Pryde's superior in the process. Numerous other Imperial officers were also stationed on the ship by the time of the Battle of Endor.
The Steadfast was initially referenced in current Star Wars canon inside of Pablo Hidalgo's 2019 reference book, Star Wars: The Rise of Skywalker: The Visual Dictionary, which was released alongside the sequel trilogy film, Star Wars: Episode IX The Rise of Skywalker. The Steadfast was initially a creation for the Star Wars Legends continuity, with its first appearance in the fourth issue of the Star Wars: Crimson Empire comic-book series. The issue was written by Mike Richardson alongside Randy Stradley, with illustrations from Paul Gulacy, and was published by Dark Horse Comics on March 18, 1998.
According to The Rise of Skywalker: The Visual Dictionary, Enric Pryde was assigned to the Steadfast in 6 BBY and remained on board until it was destroyed in 5 ABY, which means he spent eleven years serving on the Star Destroyer. "The Steadfast Soldier," a short story by Adam Christopher published within the 2023 anthology From a Certain Point of View: Return of the Jedi, which is set during 4 ABY, further supports this timeline by stating that Pryde had been serving on the ship for a decade. However, the April 20, 2021 Star Wars Encyclopedia booklet entitled "The First Order" states that Pryde served on the Steadfast for five years as part of his Imperial officer training. The 2022 English translation corrected this inaccuracy by stating that he was assigned to the ship within five years of completing that training.