The Three Prime Minister died In office were

Jawahar Nehru (May 1964) 

(15 August 1947 - 27 May 1964).

Lal Bahadur Shastri (January 1966) 

(9 June 1964 - 11 January 1966).

Indira Gandhi (October 1984)

(24 January 1966 - 24 March 1977) - (14 January 1980 - 31 October 1984).