The first elected Prime Minister was Bishweshwar Prasad Koirala

Bishweshwar Prasad Koirala was born in Varanasi to father Krishna Prasad Koirala, a follower of Mahatma Gandhi. When asked how he became interested in politics, Koirala said, "There was politics in the blood of my family. My father had to leave Nepal when I was three years old. Everyone in the family had a warrant of arrest against him; our entire property was confiscated. We were in exile in India for twelve years [1917–1929] so I had my schooling in India, and thereafter I joined my college there." The British Raj charged him and his brother, 

Matrika Prasad Koirala, for having contacts with terrorists in 1930. They were arrested and set free after three months. Because of this, Bishweshwar began to study in Calcutta at Scottish Church College per his father's wishes. Towards the end of 1930, he left the college and returned to Banaras. In 1932, he completed his intermediate level of studies. His father again insisted that his son join Scottish Church College in Calcutta. So for the second time, he joined the college, but left it soon after. In 1934, he completed his bachelor's degree in economics and politics from Banaras Hindu University.

 After earning his degree at the Banaras Hindu University, he later took a degree in law at the University of Calcutta in 1937 and practiced law for several years in Darjeeling. While still a student he became involved in the Indian nationalist movement, and in 1934 he joined the Indian National Congress. During World War II he was interned by the British in Dhanbad for two years (1942–1944). Political career Following his release, with Indian independence imminent, he set about trying to bring change to Nepal. In 1947 he founded from India the socialist Nepali National Congress, which in 1950 became the Nepali Congress Party. In 9 March 1947, Koirala crossed over to Nepal for helping brother Girija Prasad Koirala instigate Biratnagar jute mill strike. 

He was arrested along with Girija Prasad Koirala and four other National Congress leaders and taken with his fellow agitators to Kathmandu via a 21days long, slow walk across the hills. The prisoners' march attracting much attention and helping to radicalise the peasants whose villages lay en route. The Koirala along with other detanies were kept in a Kathmandu bungalow but were soon released after a 27-day hunger strike, popular protests, and by the request of Mahatma Gandhi in August 1947 B.P. went back to India, and began looking for arms to storm Kathmandu.Finally Koirala led the Revolution of 1951 which overthrew Nepal's 104-year-old Rana regime. 

The last Rana prime minister was dismissed in October 1951 when the Rana-Congress coalition cabinet (in which Koirala served for nine months as the Home minister) broke apart. Koirala then concentrated on the developing Nepali political structure. King Mahendra responded with a new constitution enabling free parliamentary elections to take place in 1959. Only a fragmented parliament was expected, but Koirala's Nepali Congress scored a landslide, taking more than two-thirds of the seats in the lower house. After several weeks of significant hesitation, Mahendra asked Koirala to form a government, which took office in May 1959. Koirala led his country's delegation to the United Nations and made carefully poised visits to China and India, then increasingly at odds over territorial disputes. 

Yet, he was in trouble at home almost from the beginning. His land reform measures, especially the revision of the tenancy laws so easily passed by parliament, deeply offended the landed aristocracy which had long dominated the army. King Mahendra, on 15 December 1960, suspended the constitution, dissolved parliament, dismissed the cabinet, imposed direct rule, and for good measure imprisoned Koirala and his closest government colleagues. Many of them were released after few months, but Koirala, though he was suffering from throat cancer, was kept imprisoned without trial until 1968. In 1968 then the Prime Minister Surya Bahadur Thapa, who led the liberal group in the Rastriya Panchayat, played a significant role in releasing B. P. Koirala from prison. Later in June, Mr. Thapa had to resign because of pressure from the hardliner in releasing Mr. Koirala from prison. Then he was finally left on a self-exile to live in Banaras.