The centre-left leader has overtaken Prime Minister David Cameron in the odds with the main betting shop firms -- even though the Conservatives remain the bookmakers' favourites to win the most seats.
Labour leader Miliband is 8/15 to be prime minister on August 1, meaning bookmakers think there is a 15 in 23 (65 percent) chance of this outcome.
Centre-right Tory leader Cameron is 11/8, meaning there is an eight in 19 (42 percent) chance of this happening.
Cameron's party is favourite to win most seats in parliament's 650-member lower House of Commons, though neither party is thought close to a 326-seat majority -- a hung parliament is now 1/10.
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"It seems illogical, but we are taking enough bets to cut our odds for Ed Miliband to be in Number 10 on August 1 from 8/11 to 8/15," said William Hill spokesman Graeme Sharpe.
While the Tories are 2/5 to win the most seats, Labour are 15/8.
As for the general election outcome, a Labour minority government is 13/8; a Conservative minority government 11/4.
A Conservative-Liberal Democrat coalition -- the current set-up -- is 6/1.
A coalition involving the SNP is 7/1, as is a Labour-Liberal Democrat coalition; a Conservative majority is 15/2, while a Labour majority is 22/1.