Mamun has a Bangladeshi father and a Russian mother. Her mother is a former rhythmic gymnast. Mamun began training in rhythmic gymnastics when she was seven years old. As a junior gymnast, Mamun represented Bangladesh for one year. As a senior gymnast, she represented Russia. Mamun became a senior gymnast in 2011. That year, she won a bronze medal in the all-around and a gold medal in ball finals at the Montreal World Cup. In 2011, she was ranked twenty-second in the world. In 2012, Mamun won three bronze medals at the Deriugina World Cup. She also won the all-around gold at the Sofia World Cup, and won the team gold medal at the Aeon Cup. Mamun was ranked seventeenth in the world in 2012. She did not compete at the 2012 London Olympics.