Thapa started his political journey in 2028 BS. He joined CPN-UML in 2049 BS and was elected the party's district secretary in 2074 BS. Thapa became the party's district chairman in 2065 BS. He became Karnali Province chairman of the CPN (Unified Socialist) following the party split in 2078 BS.
He was elected constituent assembly member in 2070 BS and province assembly member in the 2074 elections. Thapa served as the Minister for Physical Infrastructure for six months in 2077 BS.