Anil Basu of the CPI-M won the Arambagh constituency of West Bengal by 592,502 votes in the 2004 general election, according to EC data.
Among the other top winners are Lok Janshakti Party chief Ram Vilas Paswan who secured a margin of 504,448 from Bihar's Hajipur in 1989 and 424,545 from the same constituency in 1977.
In the current 2014 election, CPI-M nominee and trade union leader Sankar Prasad Datta recorded a difference of 503,486 votes on the Tripura West seat against Congress candidate Arunoday Saha, a former vice chancellor of the Tripura University.
In the tribal reserved East Tripura seat of the same state, CPI-M candidate and Tripura's forest and rural development minister Jitendra Choudhury defeated Sachitra Debbarma of the Congress by 460,548 votes.
In 1984, Rajiv Gandhi won by a margin of 314,878 from Amethi in Uttar Pradesh.