Despite trailing the opposition Conservatives by 10 points in the latest opinion poll, Brown will tell members of his center-left party that an historic fourth consecutive election victory is still within their grasp.
We can beat them, we must beat them and we will beat them, Brown will say in a speech to the party in which he plans to lay out his election strategy. His office released extracts of the speech in advance.
With Britain saddled with a record budget deficit after the worst recession in more than 50 years, the main parties have effectively already begun the election campaign with clashes over the economy and public spending.
Brown, who has struggled to quell dissent within his party since replacing Tony Blair in 2007, will seek to portray the Conservatives as a party of austerity. Their leader David Cameron has said he will cut public spending faster and further than Labour if he wins the election due by June.
We will contrast Labour -- the party of aspiration -- with the Tories, the party whose only pledge to the mainstream majority is one of austerity, Brown will say.
Financial markets are watching for details about how the next government will cut the budget deficit.
Public borrowing is set to hit 178 billion pounds ($284 billion) this year as the government spends heavily to ease the country through a recession that has cut economic output by 6 percent and slashed tax revenue.
Brown also faces criticism over Britain's military involvement in Afghanistan, Labour lawmakers' role in an expenses scandal and persistent doubts about his leadership.
After dismissing a plot by two former ministers to oust him last week as a form of silliness, Brown will refocus his election campaign on the economy, education and aspiration.
He will seek to put on a united front by appearing on stage with an election team that includes deputy leader Harriet Harman and his influential Business Secretary Peter Mandelson, seen by many as his real deputy.
Schools Secretary Ed Balls, one of Brown's closest advisers, urged party members to stop the in-fighting that has marred much of Brown's time in office. The best way to give them (the Conservatives) a mandate by default is to turn on ourselves, Balls told the Financial Times in an interview.
A YouGov poll for the Sun newspaper suggested nearly half of voters are unhappy with Labour's record since Blair swept to power in 1997. Forty-four percent said Labour had been poor or terrible, while 35 percent said it had been fair and 15 percent thought it had been good.