A faithful lieutenant of Brosin Underground leader Randle Clanse, Marn led the largest of the four teams in the Brosin Underground (which must have included more than thirty men). Marn's team operated in Reyno Valley and Nihun Valley,they attempted to harass the Corporate Sector Authority's industrial activities on Brosi, particularly the Zinsian processing plants.
Due to the Underground's efficiency, the Rebel Alliance was afraid of the CSA increasing its security, which could have led to the discovery of Rebel underground agents, or of a Rebel ten-men cell led by Abil Filorin. As of 2 ABY, Filorin had been trying to make contact with Marn, but found it very difficult. Even then Filorin doubted he could really convince Marn to change the Underground's plans.