Sir Keir Starmer will promise to prioritise security for families and the country during his first party conference speech as Labour leader.
In an online broadcast on Tuesday, he will appeal to voters who abandoned the party at December’s election that “we love this country as you do”.
He will ask them to return to Labour, stressing it is “under new leadership”.
But the Conservatives have accused him of “refusing to take a position” on important issues facing the country.
Sir Keir will tell party members it is time to “get serious about winning”, as he addresses them on the final day of Labour’s four-day annual conference.
The online event replaces the party’s traditional party conference due to be held in Liverpool, which was cancelled due to the Covid-19 pandemic.
Sir Keir will say he wants Britain to be the “best country to grow up in and the best country to grow old in. A country in which we put family first.”
Speaking from Doncaster, he will list “security for our nation, our families and all of our communities” as “values I hold dear”.
He will vow to listen to voters who abandoned Labour at last year’s election, when the party was swept aside by the Conservatives in its traditional heartlands.
Sir Keir replaced Jeremy Corbyn as leader in the contest that followed the poll, where the party won fewer Commons seats than any election since 1935.
“Trust takes time. It starts with being a credible Opposition, with taking the job seriously. That’s what we will do,” he is expected to say.
Addressing ex-Labour voters who switched to the Conservatives, he will add: “I ask you: take another look at Labour. We’re under new leadership.”
On the economy, the Labour leader will repeat calls for “properly funded” public services and “huge investment” in skills to create work opportunities.
He will also call for action to tackle climate change, and for the government to develop a new strategy to close gaps in education inequality.
And he will pledge to work “hand-in-hand” with both the private sector and trade unions in a bid to create “high quality jobs”.
Shadow foreign secretary Lisa Nandy told the BBC there had been a “real change in tone and approach” under Sir Keir’s leadership, with the party focused on “listening to what people have to say and acting on the very real problems they have in their lives”.
Pressed during an interview on BBC Radio 4’s Today about what substance there was behind the rhetoric, she suggested in foreign affairs the party was prioritising “standing up for British interests” and was determined to bring the country together after years of bitter divisions over Brexit.
But ahead of the event, Sir Keir has been warned against “watering down” the “radical policies” of his leadership campaign by the Labour-affiliated Fire Brigades Union.
The union, one of the more left-leaning of the 12 affiliated to the party, called for Sir Keir not to “cede any ground” to the Conservatives.
In an interview with the BBC, its general secretary Matt Wrack added that he had not “heard Keir make that case” since becoming Labour leader.
Ahead of Sir Keir’s speech, Conservative co-chairman Amanda Milling said: “If you take another look at Labour, the leadership may be new, but the attitudes to Brexit, immigration and the economy remain the same.
“For all his platitudes, the reality is that Sir Keir refuses to take a position on the most important issues facing our country, always preferring to carp from the sidelines.”