His father, Kaji Bal Narsingh Kunwar, was in court the day Rana Bahadur Shah was murdered by his own half-brother Sher Bahadur Shah; as a retaliation Bal Narsingh killed him on the spot. For this action, he was rewarded with the position of Kaji, which was made hereditary in his family, also he was the only person allowed to carry weapons inside the court. He was the great-grandson of Ram Krishna Kunwar, a great military leader at the times of King Prithvi Narayan Shah. Through his mother Ganesh Kumari, he was related to the aristocratic Thapa dynasty of PM Bhimsen Thapa, which helped him enter the royal court at a young age. Through his maternal grandmother he was related to the aristocratic Pande family as his maternal grandmother Rana Kumari was the daughter of Kaji Ranajit Pande, an influential royal courtier.

Bal Narsingh Kunwar was appointed as the bodyguard of Rana Bahadur Shah. When Shah was attacked on the 24th of April, 1806, he was working at the same spot. Bal Narsingh Kunwar's second wife Ganesh Kumari was the sister of Mathabarsingh Thapa. Jung Bahadur was born in Langantol of Kathmandu. In those days the Thapas had influence over the administration of Nepal. From an early age, Jung Bahadur showed interest in courageous deeds. When he was 11 years old he was married to Prasad Laxmi, the daughter of Prasad Singh on the 1st of May, 1828. His father then went to Dhankuta and took his sons with him. In 1833, Bal Narsingh moved to Dadeldhura where Jung Bahadur accompanied him and was admitted in the Military. When Bal Narsingh moved to Jumla in the year 1835, Jung Bahadur was already promoted to the rank of Second lieutenant. In 1837 when Bhimsen Thapa was dismissed, all his relatives were freed from the services. In this course, Bal Narsingh and Jung Bahadur too were dismissed from their services and their properties was seized. This incident made it difficult for Bal Narsingh to fulfill even the fundamental necessities of his large family. Jung Bahadur then went to Varanasi in search of work. There he wandered around to no avail. After a brief stay there, he returned to the Terai to work as a Mahout, but there too, he couldn't achieve any success. In 1839 he returned to Kathmandu where his wife and infant son had already died.

In 1839 Jung Bahadur was married to the daughter of Kaji Sanak Singh. Jung Bahadur received 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.

After a while, Jung Bahadur was transferred from the Prince's group back into the King's. There he was appointed as a Kaji and was sent to the office of Kumarichowk. There he got an opportunity to properly understand the financial transactions of Nepal.

Jung Bahadur was known to be extremely ambitious. During those days, the youngest Queen was the actual ruler of the country with King only of name. Gagan Singh Bhandari was closest to the queen. Jung Bahadur had managed to please the Queen, the Prince and the Prime Minister with his diligent efforts. He had also managed to influence Henry Lawrence and his wife Honoria Lawrence.

When Mathavar was still the Prime Minister, a cousin of Jung Bahadur was sentenced to death penalty. Jung Bahadur had requested Mathavir to convince the Queen to excuse his cousin but Mathavar denied. This had resulted in Jung Bahadur holding grudge against him.

Jung Bahadur befriended Pandit Bijayaraj who was the internal priest of the palace, and from him he started to gain valuable information about the Durbar. He had also managed to befriend Gagan Singh Bhandari.

After assasinating Mathavar Singh, the queen gave Jung Bahadur the rank of a General and included Gagan Singh in the council of ministers.

Kot massacre

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.

By 1850 Jung Bahadur had eliminated all of his major rivals, installed his own candidate on the throne, appointed his brothers and cronies to all the important posts, and ensured that major administrative decisions were made by himself as prime minister.^[10]

After the Massacre, on the 15th of September the Queen appointed Jung Bahadur as the Prime Minister and the Commander-in-chief. After meeting with the Queen and the King, Jung Bahadur went to meet the Resident at the British Residency. There he informed the Resident about the massacre and also convinced him that the new government will be a great friend of the English. In the 23rd of September all officers of military and bureaucracy were called upon to their respective offices within 10 days. Then, Jung Bahadur appointed his brothers and nephews to the highest ranks of the government. ^[10]

Bhandarkhal Massacre

The Queen commanded Jung Bahadur to remove Prince Surendra from the rank and declare Radendra as the new Prince but Jung Bahadur ignored it which resulted in Queen holding vendetta against him. A few people had survived the Kot Massacre who were secretly planning to avenge Jung Bahadur. The Queen secretly contacted them and conspired to assassinate Jung Bahadur. A plan was formed to do so in a gathering to be organized in the garden of Bhandarkhal situated at the eastern end of the palace.

Jung Bahadur had already placed his spies inside the palace to gather information about the Queen and the events in the palace. These spies were handed the duty of informing Jung Bahadur about the happenings in a secret manner. A certain Putali Nani whom Jung Bahadur had already taken in his side also worked inside the palace and she informed Jung Bahadur about the conspiracy.

After receiving a command from the Queen to come to Bhandarkhal, Jung Bahadur took his fully armed troops and headed towards the garden. Birdhwaj was given the duty to bring Jung Bahadur in time. When he reached to the temple of Jor-Ganesh, he saw Jung Bahadur approaching with the troops. Sighting him, Jung Bahadur signaled Capt. Ranamehar and Ranamehar killed Birdhwaj. The troops then marched towards Bhandarkhal where seeing Jung Bahadur approach fully armed with his troops, the conspirators started to flee. 23 people were killed in the massacre while 15 escaped. ^[11]The next day, everything was s