The Prime Minister will make a last-ditch bid to save his embattled leadership by highlighting his actions to rescue the economy from a major banking collapse.
And he will unveil new policies on antisocial behaviour, including the rolling out of family intervention projects, modelled on a scheme in Dundee. But his speech will come against a backdrop of falling poll ratings, with Labour now behind the Liberal Democrats, according to the Ipsos Mori poll.
It is the first time Labour has been in third place since February 1982, when the party was led by Michael Foot.
The latest survey also suggests the Tories have lost some support to the Lib Dems.
However, Ipsos Mori pointed out the Lib Dems traditionally enjoyed a "bump" in the polls after their annual conference, and Labour will be hoping for their own bounce at the end of this week. The headline figures are based on those who say they are "certain" to vote at the next general election.
Results across Scottish constituencies would be different, however, with much of the support that goes to the Conservatives in England being taken up by the SNP in Scotland.
Mr Brown's Brighton speech comes as activists have been put on a war footing and told to prepare for a May general election, according to a secret document obtained by The Scotsman.
Business Secretary Lord Mandelson yesterday tried to boost morale with a rousing speech that earned a standing ovation and a back-slap from a beaming Prime Minister. Lord Mandelson, the de facto deputy prime minister, said: "If I can come back, we can come back."
He told delegates: "I came into politics to help remake the Labour Party as a party of government. My relationship with Gordon was formed when people said we'd never form a government again.
"It made us not just modernisers but fighters – and certainly not quitters. That spirit still burns as brightly within us now as it did then."
He went on: "We may be the underdogs, but if we show the British people that we have not lost the fighting spirit and appetite for change which has defined this party throughout its history, then we can and will win."
Today, Mr Brown will deliver his keynote speech, which will highlight his economic stewardship whilst acknowledging his own leadership troubles.
With his dismal opinion poll approval ratings, Mr Brown will make the fightback the central theme of his speech, while also highlighting his record on the economy.
A Labour Party source said Mr Brown's policy announcements would also put pressure on the SNP government in Edinburgh to declare whether it would find the funds to make equally bold claims for residents north of the Border.
And in a bid to woo Middle England, Mr Brown will pledge that no cancer sufferer should wait for more than a week to see a specialist.
The party has spent much of the conference attacking the Conservatives and their leader, David Cameron. In his speech yesterday, Chancellor Alistair Darling also turned his fire on the Tories, whom he accused of "playground politics".
He warned that voters faced a "big choice" in the election between a Tory party that would "relish" slashing public spending and Labour, which would protect front-line services. Mr Darling praised Mr Brown's decisive moves to counteract the financial crisis, while the Tories, he said, had called it wrong.
"If we followed the Tory route now, recovery would be put at risk, prospects for growth damaged, borrowing would, in the long-run, be greater," he told the conference.
The next election, he said, would see Britain facing a choice – "maturity and experience against the politics of the playground".
Meanwhile, Scottish Secretary Jim Murphy warned that a vote for the SNP could usher in a Conservative government through the back door.
He suggested the campaign slogan could be "Vote Salmond, Get Cameron", adding: "But we will put Vote Labour first." Mr Murphy branded Mr Cameron "the most superficial Conservative leader in living memory".
Mr Brown's fightback speech comes as a secret handbook reveals the party is planning for a May election – with the date most likely to be 6 May, the same day as local elections.
Labour can run until 3 June without calling an election, but unless there are moves for a snap poll, the briefing given to candidates clearly shows the party preparing for May.
Candidates are urged to start their Twitter and Facebook campaigns as early as next month.
Activists are given only 17 days off between now and the general election according to a timetable in the document, "A Day by Day Planner to Your General Election Campaign".
By January, activists are urged to update their campaign plan and message. They are also told to "agree and launch three-month campaign" that month.
The document suggests the Chancellor's Budget will be unveiled in the week of 16 March. As the Budget is held on a Wednesday, the most likely date is 17 March.
The only day off that activists get in December is Saturday the 5th – presumably to do their Christmas shopping.
Labour has not entirely ruled out an earlier poll, however, and candidates are told to refer to a "brief election campaign" book if the decision is taken to call a snap election. Such a move is looking increasingly unlikely, though, as Labour will want to wait for any signs of economic recovery to help its cause.
Last night, a Labour Party spokeswoman said of the campaign guide: "This is just a best-practice guide on various campaigning options between now and the last possible date for a general election. It is for the Prime Minister to decide when the election will be and he has made no announcement."
John Curtice, professor of politics at Strathclyde University, said he expected Labour to go on "until the bitter end", but an earlier snap poll was possible.
Prof Curtice also cautioned against over-interpreting the Liberal Democrats popularity: "One does not know until the middle of October whether any of the post-conference bounce is durable. It does indicate however, that the Labour Party is in deep trouble and if the Lib-Dems were to have a good campaign, the Labour Party could be relegated to third place."
On the General Election date, Prof Curtice said: "Labour's clearly playing the long game, it is expected they will do the decent thing and wait until the local elections on May next year, but if the polls were to turn around in March, they may decide to go more quickly. But we are expecting them to go on until the bitter end."
Meanwhile, a separate poll for BBC2's Newsnight last night found almost two-thirds of voters saying their view of the Labour Party has worsened since Mr Brown took over as leader.
Among Labour voters, 55 per cent said their opinion of the party had gone down, while only 8 per cent said their opinion had gone up. Some 37 per cent said their opinion remained the same. Sixty-seven per cent did not approve of the way Mr Brown was doing his job, with 29 per cent saying they approved.
Elsewhere, BBC interviewer Andrew Marr insisted he had no intention of apologising for asking Mr Brown whether he was dependent on prescription drugs "to get through".
The BBC said it had received about 200 complaints following Mr Brown's appearance on the Andrew Marr Show on Sunday.
It is understood no formal complaint has been made by No 10 to the BBC, though many in Labour's senior ranks are known to be furious about the question, which drew on unconfirmed speculation on the internet in recent weeks that Mr Brown has been taking anti-depressants.