Bhimsen Thapa is regarded as the first Prime Minister of Nepal.
Some historians recognize Damodar Pandey as the first Prime Minister of Nepal since Damodar served as a Kaji during the reign of King Prithvi Narayan Shah.
The first elected Prime Minister was Bishweshwar Prasad Koirala, in 1959. The first Prime Minister after restoration of Democracy in 1990 was Krishna Prasad Bhattarai. He was interim govemnment chief.
Girija Prasad Koirala was the first elected Prime MIinister after the restoration of democracy in 1990 and country became constitutional Monarchy. The monarchy was aboslised in 2008 and Constituent Assembly (CA) is formed with 601 members.
Names of all Prime Ministers of Nepal
Source:wikipedia and other internet sources