He was born as the youngest son of one of the leading Gorkhali Bharadar (state-bearing officer) Birabhadra Thapa.

He was the grandfather of the first titular Prime Minister of Nepal Mathabarsingh Thapa, Queen Mother Tripurasundari of Nepal, Colonel Ujir Singh Thapa and great-grandfather of Maharaja Jang Bahadur Kunwar Ranaji, Bam Bahadur Kunwar, Ranodip Singh Kunwar and other Jang brothers & their descendants, all through his second son Nain Singh Thapa.

[1] He fought at Kerung Axis during the Sino-Nepalese War under the leadership of Chautariya Balbhadra Shah and alongside Kirtiman Singh Basnyat and Bhotu Pande.

[1] When Rana Bahadur Shah abdicated the throne in 1799, Sanu Amar Singh and his son Bhimsen Thapa were promoted from Subedar to the rank of Sardar.

[2] He was subsequently replaced by his teenager grandson Ujir Singh Thapa as Governor of Palpa.