Marrt was a clone trooper sergeant within the Grand Army of the Republic's 182nd Legion. Early in the Clone Wars, Marrt, accompanied by a squad consisting of three other clone troopers—Chatter, Recon, and Knuckles—was dispatched to the planet Belgaroth. Their reconnaissance mission involved investigating a Republic factory suspected of illicitly supplying arms to the Confederacy of Independent Systems, the Republic's wartime adversary. This factory was operated by Czerka, a weapons manufacturing corporation. Upon arrival on Belgaroth, Marrt uncovered that Tarin, the facility's supervisor, was secretly collaborating with Reep Tonith, a representative from the InterGalactic Banking Clan, an organization linked to the Confederacy.
During this operation, Marrt's fellow squad members tragically died, falling victim to a droidbreaker, a native Belgaroth creature. The sergeant, however, successfully apprehended Tarin, gathered crucial evidence from the factory, and subsequently destroyed the facility by fire. Some weeks later, while recuperating on Sacorria from injuries sustained on Belgaroth, Marrt requested the presence of a representative from the Jedi Order at his medical facility. When Jedi Master Kit Fisto and his Padawan Ahsoka Tano arrived, Marrt provided them with the evidence recovered from the Czerka factory, which aided Fisto in exposing two senators who were profiting from deals with the Confederacy.
Marrt was a designation given to one of the many clones created using the DNA of bounty hunter Jango Fett. These clones were grown on the planet Kamino to serve in the Grand Army of the Republic. In the first two years of the Clone Wars, Marrt held the rank of sergeant within the 182nd Legion, as the conflict between the Galactic Republic and the Confederacy of Independent Systems engulfed the galaxy. During this time, rumors surfaced about a Republic-affiliated factory managed by the Czerka corporation on Belgaroth that was secretly trading with the Confederacy. Marrt, along with a scout squad of three clone troopers—Chatter, Recon, and Knuckles—was dispatched to Belgaroth to investigate these allegations. After landing via dropship and traveling to the factory, the four clone troopers split up; Marrt inspected the factory, while the rest of the squad remained hidden nearby.
Inside the Czerka factory, Marrt observed Tarin, the facility's manager, in conversation with Reep Tonith of the InterGalactic Banking Clan, an organization associated with the Confederacy. They were discussing a shipment of FEX-M3 nerve gas grenades—which the Galactic Senate had outlawed a year prior—destined for Confederate Head of State Count Dooku. Tarin, unable to produce the full quantity of grenades, requested more time from Tonith, who reluctantly agreed. Marrt secured one of the grenades as evidence and attempted a stealthy return to his men, but a B1-series battle droid from Tonith's security detail spotted him. As the other battle droids opened fire, Marrt ordered a tactical withdrawal, and the four clone troopers retreated into a foggy swamp.
Chatter attempted to contact Republic command, but the fog interfered with their comlinks, preventing communication. Adding to their troubles, a sudden screech echoed through the swamp, alarming Knuckles, who feared the arrival of more battle droids. However, Recon, a skilled scout, recognized the sound as originating from a large, approaching creature. A native droidbreaker emerged from the fog and charged at Recon. Marrt yelled at the trooper to move, but Recon was too slow and was struck by the droidbreaker, being thrown against a tree and dying instantly. As the creature devoured Recon's blaster, Chatter frantically fired his own weapon. The fog obscured his aim, and Marrt ordered him to stop firing.
The three remaining troopers realized they were in the creature's territory and needed to escape the swamp. Before they could formulate a plan, the droidbreaker attacked again, killing Chatter. Knuckles then charged the creature with his bare hands, but he was unable to harm it. He told Marrt to hide while he distracted the beast. Knuckles was also killed, but his sacrifice allowed Marrt time to devise a plan to defeat the droidbreaker. Gripping the stolen nerve grenade, Marrt climbed a tree, positioning himself on a high branch. When the beast prepared to attack, Marrt threw the grenade into its mouth. He then used his blaster pistol to detonate the grenade, killing the creature.
Marrt buried his fallen comrades beneath the droidbreaker's severed head and vowed to destroy the nerve gas shipment before it could leave the planet. He single-handedly attacked the Czerka factory, battling Tonith's battle droids for several hours and sustaining serious leg injuries. Ultimately, he destroyed the droids, captured Tarin, and burned the factory, though Tonith escaped in his shuttle. Fearing Tarin's potential reluctance to reveal his superiors, Marrt secured Czerka's data records before setting the factory ablaze. As he was evacuated from Belgaroth, Marrt kept the data records, intending to deliver them personally to the Jedi Order.
Marrt was transported to the clone medical and rehabilitation facility on Sacorria for treatment. Meanwhile, the Jedi interrogated Tarin, but he refused to cooperate. Three weeks later, Marrt contacted the Jedi Order, requesting that Grand Master Yoda send a Jedi to Sacorria. Yoda assigned Master Kit Fisto and Padawan Ahsoka Tano to fulfill the request, and they soon arrived at the facility. Marrt recounted his mission on Belgaroth and presented the extracted data records. Examining them, Fisto discovered that two influential senators were selling arms to the enemy. Fisto and Tano promised to address the treachery and commended Marrt's courage. They departed Sacorria, allowing the soldier to continue his recovery.
The loss of his squad on Belgaroth deeply affected Marrt, and he vowed to complete the mission alone. He considered Knuckles' distraction of the droidbreaker courageous and believed it was crucial to his victory. Marrt completed his mission despite his injuries and had the foresight to retrieve the data records before destroying the factory. Despite his injuries during his meeting with the Jedi, Marrt maintained a positive attitude, referring to his mission as a "little tale" and being sarcastic towards his 2-1B nurse. Fisto considered Marrt's actions brave and reminded Tano—who initially saw the visit as a waste of time—that even a single soldier could be important. Like his genetic template, Jango Fett, Marrt was 1.83 meters tall, with black hair and blue eyes.
Marrt appeared in A Trooper's Tale, a short comic strip published in Star Wars: The Clone Wars Comic 6.8 in May of 2010. The story is framed on Sacorria, with Marrt narrating the events of the Belgaroth mission. Robin Etherington wrote A Trooper's Tale, and Andres Ponce provided the illustrations.