Jung Bahadur Rana was born on 18 June 1817 in his maternal uncle’s house in Thapathali, Kathmandu. Originally, his birth name was Bir Narsingh Kunwar. He was the eldest son of Kaji Bala Narasingh and his younger wife Ganesh Kumari. Bal Narsingh Kunwar was appointed a bodyguard of King Rana Bahadur Shah.

In 1839 Jung Bahadur was married to the sister of Colonel Sanak Singh Shripali Tandon. Jung Bahadur received a decent amount of dowry from the marriage which resulted in a slight betterment in the financial condition of the family. In 1840, the King Rajendra went to Terai where coincidentally Jung Bahadur was also accompanying him. There Jung Bahadur impressed the King by displaying great courage. The King was pleased with him and immediately gave him the position of Captain. After returning, Jung Bahadur was included amongst the bodyguards of the Crown Prince. Once, in the command of the Prince he had to jump into the Trishuli River riding a horse which he did and only just survived.

The Kot massacre took place on 14 September 1846 when Jung Bahadur Rana and his brothers killed about 40 members of the Nepalese palace court including the Prime Minister and a relative of the King, Chautariya Fateh Jung Shah, at the palace armory (the kot) of Kathmandu. This led to the loss of power by King Rajendra Bikram Shah and by Surendra Bikram Shah and the establishment of the Rana autocracy.

On 12 May 1847, Jung Bahadur gave a speech in Tudikhel. There he accused the King of attempted assassination of the Prince and the Prime Minister. The Council then decided to dethrone King Rajendra deeming him mentally ill, and on the same day Surendra was crowned as the new king of Nepal.

Towards the end of 1848 a vicious battle waged between the British and the Sikhs in Punjab. After hearing the news, Jung Bahadur met with the Resident and assured of Nepal Government’s support to the British. But the Governor-General rejected the proposal fearing the possibility of the Nepali troops diverting to the side of the Sikhs at the crucial moment. Jung Bahadur then decided to demonstrate his power to the English. He was passionate for hunting but after being the Prime Minister he had not gotten an opportunity to hunt. In 1848, Jung Bahadur planned to go to the Terai with a dual purpose, one for hunting but primarily to show-off his power to the English. In 22 December, with the King and a large group alongside him, Jung Bahadur left Kathmandu. The group included thirty-two thousand soldiers on foot, fifty-two cannons, three hundred risalla, and cannons to be pulled by two hundred and fifty mules. After getting the information of this large a force nearby its boundary, the Governor-General sent a message to the Resident asking him to figure out the reality of the matter.

By 1850, Jung Bahadur had eliminated all of his major rivals, installed his own candidate on the throne, appointed his brothers and cronies in all the important posts, and ensured that major administrative decisions were made by him as prime minister.

On 21 August 1850, Jung Bahadur and the team departed towards France. There he met with the then President of France. In France too, he expressed his desire to establish a direct relationship between Nepal and France, but the French President insisted on forming the relationship through the British Embassy, as there was no diplomatic relationship between the two countries. Jung Bahadur and the team stayed at France for about six weeks. On 3 October they departed from Paris and on 6 November reached Bombay.

On 6 January 1854, the Muluki Ain was implemented around the country of Nepal. The copies of the Act were distributed around all offices, courts. The issue of this Act freed the administrators of Nepal from the confusion that had been arising from the religious laws. The decision on cases happened early.

In 1858 King Surendra bestowed upon Jung Bahadur Kunwar the honorific title of Rana, an old title denoting martial glory used by Rajput princes in northern India. He then became Jung Bahadur Rana, and the later prime ministers descended from his family added his name to their own in honour of his accomplishments. Their line became known as the house of the Ranas. Jung Bahadur remained prime minister until 1877, suppressing conspiracies and local revolts and enjoying the fruits of his early successes. He exercised almost unlimited power over internal affairs, taking for his own use whatever funds were available in the treasury. He lived in the high style of an Anglicised native prince in the British Raj, although unlike the Indian princes he was the ruler of a truly independent nation, not an ally rather than a subordinate of the British.

Begum Hazrat Mahal took refuge in Kathmandu with her 10-year-old son in 1859 Birjis Qadr and some other loyal staff. The then Prime Minister of Nepal, Jung Bahadur Rana, gave her shelter at the palace in Thapathali (which now houses an office of the Nepal Rastra Bank, Thapathali Durbar), said Samim Miya Ansari. Jung Bahadur Rana took the step despite being in good terms with the British at the time.