Since 1947, India has had fourteen Prime Ministers, fifteen including Gulzarilal Nanda who twice acted in the role. The first was Jawaharlal Nehru of the Indian National Congress party, who was sworn-in on 15 August 1947, when India gained independence from the British. Serving until his death in May 1964, Nehru remains India's longest-serving prime minister. He was succeeded by fellow Congressman Lal Bahadur Shastri, whose 19-month term also ended in death. Indira Gandhi, Nehru's daughter, succeeded Shastri in 1966 to become the country's first woman premier. Eleven years later, she was voted out of power in favour of the Janata Party, whose leader Morarji Desai became the first non-Congress prime minister. After he resigned in 1979, his former deputy Charan Singh briefly held office until Indira Gandhi was voted back six months later. Indira Gandhi's second stint as Prime Minister ended five years later on the morning of 31 October 1984, when she was gunned down by her own bodyguards. That evening, her son Rajiv Gandhi was sworn-in as India's youngest premier, and the third from his family. Thus far, members of Nehru -- Gandhi dynasty have been Prime Minister for a total of 37 years and 303 days.

Based on this passage, who was longest serving prime minister of india? Let's think fast. Stream of consciousness:
The relevant sentence in the passage is: Serving until his death in May 1964, Nehru remains India's longest-serving prime minister. So the final answer is Jawaharlal Nehru.