Ed Miliband has said Labour will "change the way the country is run and who it is run for" as he launched the party's election manifesto.
Saying he had been tested as opposition leader and was "ready" for power, Mr Miliband said Labour would be a "party of change and responsibility".
He ruled out a "shopping list of proposals", guaranteeing all policies would require no extra borrowing.
But PM David Cameron accused Mr Miliband of trying to "con" the public.
The 86-page manifesto, which is 20,421 words long, sets out Labour's main policy pledges, including:
- Raising the minimum wage to more than £8 by the end of 2019
- A one-year freeze in rail fares, costing £200m, paid for by delaying upgrades to the A27 and A358 trunk roads
- Twenty-five hours of childcare for working parents of three and four-year olds and a new right to pre and after-school help, paid for by rise in bank levy
- Freezing gas and electricity bills until 2017, so they can only fall not rise
- A £2.5bn fund for the NHS paid for largely by a mansion tax on properties valued at over £2m
- Scrapping winter fuel payments for the richest pensioners, capping child benefit rises and protecting tax credits
- A 50p tax rate on incomes over £150,000 a year and abolishing non-dom status. Rises in VAT and national insurance ruled out
- A cut in university tuition fees from £9,000 to £6,000
Speaking in Manchester, Mr Miliband said the first page of Labour's manifesto "sets out a vow to protect our nation's finances; a clear commitment that every policy... is paid for without a single penny of extra borrowing".
Labour would not promise anything it could not fund, he said, contrasting this with the Conservatives which he described as the "party of sums that do not add up and commitments that cannot be kept".
He added: "The plan we lay before you is no less ambitious because we live in a time of scarcity.
"It is more ambitious because it starts from a clear commitment to balance the books and more ambitious because it does not stop there.
"It meets the scale of the challenges we face today with not one policy funded by extra borrowing."
Mr Miliband said Labour would put the interests of working people ahead of vested commercial interests, promising to raise the minimum wage to more than £8 by 2020 and requiring the wealthiest in society to pay more in tax.
He said he would not seek to "carry on from where the last Labour government left off" but would "seek to solve the challenges of our time".
Addressing criticism of his leadership and suitability to be prime minister, which the Conservatives have made an election issue, he said: "Over the last four-and-a-half years, I have been tested.
"It is right that I have been tested for the privilege of leading this country.
"I am ready. Ready to put an end to the tired old idea that as long as we look after the rich and powerful we will all be OK.
"Ready to put into practice the truth that it is only when working people succeed, that Britain succeeds."
- Responsibility "triple lock": fully funded manifesto, cut the deficit every year, balance the books as soon as possible in next Parliament
- Extra £2.5bn for NHS, largely paid for by a mansion tax on properties valued at over £2m
- Raise minimum wage to more than £8ph by 2019
- No rise in VAT, NI or basic and higher rates of income tax
- Access to childcare from 8am-6pm for parents of primary school children
- Freeze energy bills until 2017 and give energy regulator new powers to cut bills this winter
But Mr Cameron told BBC Radio Newcastle: "When people hear Ed Miliband today they will think this is not a conversion to responsibility. It is not a conversion, it is a con."
In other election news on Monday:
- Lib Dem leader Nick Clegg says his party would not join another coalition with the Conservatives if they insisted on carrying out their proposed £12bn welfare cuts
- One hundred small business owners, some of which used to support Labour, have written a letter to the Sun saying they intend to vote Tory
- The Green Party calls for a "review" of horse and greyhound racing as it launches a national poster campaign
- Ed Miliband and Nigel Farage will be at opposite ends of the platform during the BBC's election debate on Thursday
- A new ICM poll gives the Conservatives a six-point lead over Labour while YouGov's latest poll puts Labour three points ahead
With political parties under increasing pressure to explain how they will fund their pledges, the Institute for Fiscal Studies complained on Sunday that they were making "lots of promises" without producing much detail on how to deliver them.
Carl Emmerson, the IFS deputy director, said Labour had not indicated whether cuts would be made to police, defence or local government budgets to balance the books.
Labour has said it would "do what it takes" to support the NHS but would not make any funding promises which could not be met.
It is guaranteeing that every policy is paid for without additional borrowing through a "budget responsibility lock", which would also require all the major parties to have their tax and spending plans audited by the independent Office for Budget Responsibility before a general election.
Analysis by political editor Nick Robinson
Ed Miliband's "mission" as your prime minister would, he said, be simply summed up: "I will always stand up for you."
It was one of the most powerful speeches I've seen him make.
It was, though, the front page of the manifesto with its "Budget Responsibility Commitment" and "clear vow to protect our nation's finances" which revealed his greatest fear. How can he convince voters so soon after the Great Crash of 2008 to put Labour in charge of the economy again?
He promises a "triple lock ….everything in this manifesto is funded. The deficit will be cut every year. The books will be balanced and the national debt will be falling."
The language is new. The prominence it's being given is new too and a stark contrast with that last big speech Ed Miliband made in Manchester, at the Labour Party conference, when he "forgot the deficit". The content is not though. Read Nick's blog in full.
Both the Conservatives and Liberal Democrats have pledged to eliminate the £90bn annual deficit by 2017/18.
However, while Labour promises to cut borrowing during every year of the coming Parliament, the party offers no deadline, saying it would commit to achieving a budget surplus on current spending "as soon as possible" between 2015 and 2020.
Labour's rivals said its track record was one of economic mismanagement, with Lib Dem leader Nick Clegg likening Labour's borrowing pledge to "an alcoholic, who drinks a bottle of vodka every day, claiming they have no plans for additional vodka".
UKIP leader Nigel Farage said there was no detail about how the deficit would be cut, while the SNP's Nicola Sturgeon said Scotland would see further budget cuts under Labour.
Employers group the CBI welcomed Labour's focus on fiscal responsibility but said its proposed interventions in markets such as energy were worrying.
The Conservatives and Greens are due to launch their manifestos on Tuesday, followed later this week by the Lib Dems and UKIP.
Several manifesto pledges made in 2010, including a Conservative plan to raise the inheritance tax threshold and a Lib Dem commitment for a £2m "mansion tax", did not make it into the coalition programme the two parties agreed on after the two parties went into government together.
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