PM Jawahar Lal Nehru is India's longest-serving PM, remaining in office for 16 years, 286 days. His daughter Indira Gandhi (15 years, 350 days) follows him. Dr Manmohan Singh served 10 years and 4 days as PM and Narendra Modi served as PM for 10 years and 8 days. Atal Bihari Vajpayee remained PM for 6 years and 80 days.