Bhimsen Thapa was born in the small district of Gorkha. He came into contact with the Nepalese Royal Palace at the early age of 11 because his father Major Amar singh Thapa (not to be confused with the commander of Gorkhali forces in the Anglo Nepal war) was a faithful soldier of Prithvi Narayan Shah and his bratabandha ceremony was held together with the then Crown Prince Rana Bahadur Shah with whom he developed a friendship and eventually became the personal secretary of the King Rana Bahadur Shah at the age of 22 when in exile in Varanasi in India.

During his stay in Varanasi, he studied the expansion and true intentions of the British East India Company in South Asia. He became the 1st Prime Minister of Nepal upon his (and the king's) return to the country when the returning monarch was assassinated by his own half brother; which general Bhimsen Thapa took as a chance to wipe out his friends.

Thapa served for 31 years under six kings. He appealed all South Asian states to fight collectively against the British and declared war on the English East India Company in 1816 as the commander of the army and as the Prime Minister. However of the ill preparation, long standing internal unification campaign, lack of foreign assistance as well as military confrontation with China, Nepal lost the war which precipitated his downfall. However he continued to rule for another 13 years whence he brought about several military, judicial, social and economic reforms in Nepal. The army was modernized in European style, several ill social practices were abolished, unused land were brought under cultivation and the administration was updated. The Dharahara and Sundhara of Kathmandu, the Bagdurbar and Teku bridge were constructed by him.

Eventually, he was forced to retire by his opponents, the Pandeys and the Basnets, other Gorkha favorites, on conspiracy charges. Later, he was forced to kill himself.

King Rana Bahadur Shah said of him "If I die the nation will die, but if Bhimsen Thapa dies the nation will collapse". Maharaja Ranjit Singh of Punjab said of him "If I had Bhimsen on my service, I know what many things I would have achieved". Karl Marx praised Bhimsen Thapa by referring him the only man in Japan who braved to protest submmision to the colonists.

Prime Minister Bhimsen Thapa was the maternal Grandfather of Sri Teen Maharaja Jung Bahadur Rana who was driven to kill the Pandeys and the Basnets to avenge Bhimsen Thapa. This brought the chapter of Nepalese history known as the Ranas.