The embattled Labour leader said he had learned the meaning of the phrase “what doesn’t kill you makes you stronger” following the latest round of bitter infighting within his party’s ranks.
In a speech attempting to relaunch his pitch to voters, Mr Miliband said he is driven by a desire to change the country rather than personal ambition.
Speaking in central London, he confronted the personal criticism head-on at the start of his address: “There’s a saying that goes ‘what doesn’t kill you makes you stronger’.
“As Leader of the Opposition, over the last few days I have learned what that really means.
“You need resilience in this job, you need thick skin, but above all you need belief in what you are doing.
“Not belief based on a longing to have a picture on the wall of Downing Street, not belief driven by a sense of entitlement, not belief driven by the idea that it’s somehow Labour’s turn, but belief driven by the idea of how we must change the country.
“That’s why I’m in this job, that’s why it matters to me, that’s what drives me on.
“And it is through our beliefs that we are going to win the general election.”
Mr Miliband said anyone who thought his job was hard should think about people doing “really hard jobs”.
“Shift work. Night work. Zero-hours contracts. Sixty hours a week. Two jobs, even three jobs, to make ends meet,” he said.
“For me, this election is about them. And let me just say this: I am willing to put up with whatever is thrown at me, in order to fight for you.
“That’s my duty, that’s my responsibility. That’s our duty, that’s our responsibility.
“Not to shrink from the fight. Not to buckle under the pressure. But to win.”
Mr Miliband said he was coming under pressure not because opponents thought Labour would lose, but “because they fear we can win”.
“Between now and the election they are going to use every tactic to try to destabilise, distract us and throw us off course,” he warned.
“Our task, the task for every person in this party, is simple: To focus our eyes on the prize of changing this country.”
Mr Miliband said his “core belief” was that “our country only works for the privileged few today, not for most people”.
The public was asking “why they are on zero-hours contracts while some of those at the top get away with paying zero tax”.
“The zero-zero economy we need to change,” he added.
He said he wanted to be prime minister because the country was “deeply unequal, deeply unfair, deeply unjust”.
“This inequality is not some accident. It is driven by beliefs about how you run countries and how we should run Britain,” he said.
“Wrong beliefs. Beliefs that have had their time. The belief that insecurity is the way you make working people work harder.
“The view that low pay is the only way we can compete in the world.
“The idea that markets will always get the right outcome, even if that means powerful interests have all the power.
“The notion that we cannot afford decent public services when money is tight.
“And above all, the most mistaken view of all, that the success of the country depends just on a few at the top.
“And when they do well, everyone in Britain does well. These are the failed ideas of the past.”