Koirala ya shiga siyasa a cikin 1954 wanda aka yi wahayi zuwa ga manufofin zamantakewar dimokiradiyya na Jam'iyyar Nepali. A shekara ta 1958 ya shiga cikin Bhadra Abagya Aandalon, (Civil Disobedience Movement) wanda Jam'iyyar Nepali ta kaddamar. A shekara ta 1959, ya tsunduma cikin manufofin jam'iyyar na gudanar da za ~ en dimokiradiyya. Za ~ en ya ga Bishweshwar Prasad Koirala ya zama firaministan farko na kasar. Duk da haka, Sarki Mahendra ya shirya kuma ya zartar da juyin mulki a watan Disamba na 1960 kuma ya kori Bishweshwar Prasad Koirala. Wannan ya haifar da gudun hijira na 'yan majalisar Nepali da dama zuwa Indiya, ciki har da Sushil Koirala. Ya kasance a gudun hijira na siyasa a Indiya har tsawon shekaru 16 bayan karɓar mulkin Koirala a 1960.
Shekaru 16