ICM found just 21% thought the Labour leader was performing well - down from 28% in April. More than half, 51%, said he was doing badly.
Mr Miliband's personal figures were worse than those for David Cameron, who was praised by 32%, but better than Nick Clegg's. Only 17% said the Liberal Democrat leader was doing a good job.
However, the poll found most people still believed Labour would win if a General Election was held tomorrow. Some 32% of the more than 2000 questioned thought the party would emerge victorious, while 30% backed the Tories and 16% the LibDems.
ICM director Martin Boon compared Mr Miliband's leadership to Iain Duncan Smith's spell in charge of the Conservatives.
"Ed Miliband is not in a good place. Only a fifth of voters are satisfied with his performance," he said. "It's difficult to imagine things could be any worse for him.
"He is becoming Labour's IDS and if it carries on like this it's hard not to think that we'll be seeing Conservative polling leads very soon."
At the Edinburgh Book Festival on Friday, Mr Miliband cautioned against relying on the fragile economic recovery to improve living standards for most people.