Nien Nunb was a native of Sullust, a dark volcanic planet with many mines. The SoroSuub Corporation, a leading mineral processing company, set itself up as the Supreme authority on Sullust. While SoroSubb supported the Empire, many Sullustans supported the Rebellion. Sullustans have an enhanced sense of direction, giving them advantages in memorizing maps, star charts, or coordinates. These qualities make Nien Nunb an excellent navigator and pilot.
Nien used his ship, Sublight Queen, as a trade runner for SoroSuub. During one of his runs to outlying mining systems, he met Lando Calrissian. When the SoroSubb Corp. decided to support the Empire, Nunb left. Nien Nunb then robbed SoroSuub consignments and started shipping them to the Rebels. After being attacked by Imperial Forces, and losing his ship, he decided to join the Rebellion full time.
Lando Calrissian picked Nien Nunb to copilot the Millennium Falcon in the attack on the 2nd Death Star. The rebel fleet attacked the Death Star, even with it's shields up. After the shields were knocked out, the Falcon and an X-wing made it into the reactor core. After the reactor was blown up, they escaped safely.
Shortly after the Destruction of the 2nd Death Star, Nunb started to copilot the Falcon with Han Solo & Chewbacca. Together they did several different missions. Seven years after the Battle of Endor, Lando reopened the spice mines of Kessel. Rather then using slaves, Lando asked Nien Nunb to run the installation. Nien agreed, and used droids to work the mines. If the Rebels ever needed help from him again, he would be glad to help.