Nembang is active in politics since 2028 BS. He was elected Chairman of the All Nepal National Free Students Union of Ilam Multiple Campus in 2028/29 BS. He became UML standing committee member in 2075 BS. Currently, Nembang is the UML vice-chairman.
He was a National Assembly member from 2048 BS to 2052 BS. Nembang was elected from Ilam-2 in the House of Representatives elections held in 2056 BS. He was elected from the same constituency in Constituent Assembly elections held in 2064 BS and 2070 BS. Nembang was re-elected from Ilam-2 in the last federal polls.
Nembang served as Speaker of the resorted House of Representatives in 2063 BS. He became Speaker of the House of Representatives in 2064 BS and served as Constituent Assembly Chairman/Speaker in 2065 BS and 2070 BS. Nembang was re-elected Speaker in 2072 BS.
Nembang served as State Minister for Law and Parliamentary Affairs in 2051. He also worked as Minister for Law, Justice and Parliamentary Affairs, Minister for General Administration and Minister for Local Development on different occasions.