Jeremy Corbyn pledged to deliver "a kinder politics, a more caring society" as he used his first conference speech as leader to urge the Labour Party to unite behind him to oppose "the misery on offer from the Conservatives".
But he set the stage for confrontation with his own shadow cabinet by declaring that his landslide victory in the summer's leadership election gave him a "mandate" to oppose the renewal of Britain's Trident nuclear deterrent.
His comment put him at odds with shadow defence secretary Maria Eagle, who backs Trident and is conducting a review of Labour's defence policy.
"There is one thing I want to make my own position on absolutely clear, and I believe I have a mandate from my election on it," Mr Corbyn told Labour's annual conference in Brighton.
"I don't believe that £100 billion spent on a new generation of nuclear weapons taking up a quarter of our defence budget is the right way forward. I believe Britain should honour our obligations under the non-proliferation treaty and lead in making progress on international nuclear disarmament."
His reference to the mandate provided by his 60% support in the leadership ballot was a late addition to the 59-minute speech, and did not feature in copies of the text circulated shortly before he took to the stage.
And his position was immediately challenged by backbencher John Mann, who said Mr Corbyn was "entitled to take a different point of view" but added: "I'm sure as leader he will feel obliged to follow the party policy."
Mr Corbyn held out an olive branch to Labour moderates who declined to serve in his shadow cabinet by insisting that he will not impose his own views on the party and was ready to listen to advice.
But he also made a commitment that party members will have "the final say" on policy and that there will be no veto either for him, his shadow cabinet or Labour MPs, many of whom are known to be concerned about any move towards unilateral disarmament.
In a speech which was light on policy and made no direct reference either to the deficit or immigration, Mr Corbyn focused on challenging the Conservative case for austerity and setting out his promise to create "a society for the majority".
He sent out a message to voters: "You don't have to take what you are given... Our Labour Party says No."
Under his leadership, Labour would "challenge austerity" and be "unapologetic about reforming our economy to challenge inequality and protect workers better", he said.
He announced plans for maternity and paternity pay for the self-employed, confirmed he would take railway services back into public ownership as franchises come up for renewal and make schools accountable to local authorities, and said Labour would pursue a "very large and very active" council house building programme, as well as tackling land hoarding and land speculation.
Labour would fight child tax credit cuts "every inch of the way" and expose Chancellor George Osborne's announcement of a £7.20-an-hour National Living Wage as an "absurd lie" which fell far short of a true living wage.
Branding Mr Osborne's austerity programme as "the outdated and failed approach of the past", he said it had delivered "an economy that works for the few, not for the many" and had left Britain "ill-prepared ... to face another crisis".
Rather than the Tories' "unbalanced, unstable" recovery built on house price inflation and private debt, Labour's economic policy would put "investment for the future" at its heart, with a new National Investment Bank making money available for infrastructure projects.
The Conservative Government existed "to protect the few and tell all the rest of us to accept what what we're given", offering tax breaks to the hedge funds which have lavished donations on the Tories since David Cameron became leader, while "cutting jobs ... slashing public services ... vandalising the NHS ... putting half a million more people into poverty", said the veteran left-winger.
"They want us to believe there is no alternative," he said.
"They expect millions of people to work harder and longer for a lower quality of life.
"Our Labour Party says No.
"The British people never have to take what they are given. And certainly not when it comes from Cameron and Osborne."
After coming under attack for his failure to sing the national anthem at a Battle of Britain commemoration, Mr Corbyn insisted that his political beliefs were driven by love of his country and "shared majority British values" of fair play, solidarity and respect.
In a bid to counter claims that he would fail to support the armed forces as prime minister, he said Britain needed "strong, modern military and security forces to keep us safe", but added that: "The best way to protect the British people against the threats we face to our safety at home and abroad is to work to resolve conflict."
Contrary to some predictions, he did not use the speech to apologise for the Labour Party's role in taking Britain to war in Iraq, but said that taking the military action on a false prospectus "didn't help our national security".
And he signalled his opposition to any Government attempt to secure Parliament's approval of military action in Syria, saying: "The answer to this complex and tragic conflict can't simply be found in a few more bombs."
None of Mr Corbyn's predecessors as Labour leader was present for his address. But he made a point of praising Ed Miliband for his "courage and dignity", as well as offering his thanks to Harriet Harman - who stood in as leader following the election - and his three leadership rivals, Liz Kendall, Yvette Cooper and Andy Burnham.
He won a standing ovation as he concluded by telling activists: "Don't accept injustice, stand up against prejudice.
"Let us build a kinder politics, a more caring society together. Let us put our values, the people's values, back into politics."
True to his low-key style, Mr Corbyn made few concessions to conference razzmatazz, taking to the stage in a red tie and jacket with little build-up. Wife Laura Alvarez watched from the audience but did not join him on stage.
The speech won loud plaudits from unions, with Unite leader Len McCluskey hailing him for "bringing integrity back" and GMB general secretary Paul Kenny saying his "no whistles, no bells" style would "resonate with the public who have been disillusioned with Westminster politics".
But CBI director general John Cridland said the business group "doesn't recognise Mr Corbyn's characterisation of the economy", while John Longworth of the British Chambers of Commerce said some businesses may share the Labour leader's diagnosis of Britain's economic challenges but "disagree with his proposed cure".
For Conservatives, Justice Secretary Michael Gove said: "Labour have confirmed that they are a threat to our national security, our economic security and to the security of every family in Britain.
"The Labour leader's policies to borrow more, print money and put up taxes on people's jobs and incomes would wreck our economy."