Theresa May will close the Conservative conference by declaring Britain's post-Brexit future is "full of promise" and insisting her party remains "on the side" of hard-pressed families.
The PM will tell the Tory faithful the country's "best days lie ahead of us".
She will also announce that
fuel duty will be frozen for the ninth year in a row in the Budget later this month.
Her speech comes after Boris Johnson launched a fresh broadside against her Chequers plan for trade with the EU.
The ex-foreign secretary told a packed meeting on Tuesday it was "constitutional outrage" that would lead to the UK being humiliated.
The conference has been overshadowed by tensions over Brexit, with the prime minister sticking by her Chequers plan, which would see the UK retain close links to the EU in trade in goods, but not services, despite criticism from all sides.
Mrs May will be hoping her big keynote speech goes more smoothly than last year when a coughing fit forced her to stop on several occasions and she was also interrupted by a prankster who handed her a mock P45.
The BBC's political editor Laura Kuenssberg said it was the PM's task to show she could "change the conversation" and demonstrate that Brexit would make a positive difference to people's lives at a time when her future was an "open question" within the party.
She will use her speech to try to strike an optimistic note, and is expected to say: "I passionately believe that our best days lie ahead of us and that our future is full of promise.
"Don't let anyone tell you we don't have what it takes: we have everything we need to succeed."
She will re-iterate her commitment to helping people on low incomes by ruling out any increase in fuel duty in the Budget on 29 October.
There has been speculation that the annual freeze, in place since 2010, may come to an end, with an inflation-linked rise used to pay for the £20bn in extra annual funding promised for the NHS.
The prime minister will also launch an attack on Labour leader Jeremy Corbyn, claiming millions of non-Tory voters were worried about "what he has done to Labour"
The Conservatives, she will say, must show they are a "party not for the few, not even for the many, but for everyone who is willing to work hard and do their best".
"One that puts the national interest first. Delivers on the issues they care about. And is comfortable with modern Britain in all its diversity.
"We must show everyone in this country that we are that party."
PM 'cross with Johnson'
Mr Johnson used his appearance on Tuesday to make the case for greater economic freedom after Brexit and lower taxes.
In response, Mrs May said the ex-foreign secretary could be relied upon to put on a "good show" but parts of his speech - which she says she did not watch - had made her "cross".
"He wanted to tear up our guarantee to the people of Northern Ireland. Northern Ireland is part of the UK," she said.
Environment Secretary Michael Gove - who unlike fellow Brexiteer Boris Johnson has stayed in the cabinet to defend Mrs May's Chequers plan - has said he is worried about the prospect of a no-deal Brexit, something the government has not ruled out.
"As a government we are preparing for any eventuality but I think it would be sub-optimal," he said at a fringe event on Tuesday evening.
Asked if Brexit was turning out the way he had expected, Mr Gove replied: "No, not quite."
He added: "I didn't expect there would be such a head of steam behind calls for a second referendum or a people's vote."
