Labour is pledging to end in-work poverty within its first full-term if it wins the next election.
In a speech later, John McDonnell will promise to tackle the issue with a “structurally different economy”, “public services free at the point of use” and a “strong social safety net”.
This includes a “real living wage” and stopping the Universal Credit roll-out.
But the Conservatives said the policies would “harm the people [Labour] claim they want to help the most”.
Poverty among people who are working has risen since the mid-1990s.
The Institute for Fiscal Studies said the proportion has gone up from 13% in 1994-95 to 18% in 2017, meaning about eight million people living in working households are in relative poverty.
A household is defined as being in relative poverty when its income is less than 60% of the average – less than £17,040 a year, on the most recent figures.
The IFS research said the rise had been partly driven by higher housing costs and lower earnings growth.
Shadow chancellor Mr McDonnell will list a number of policies – some which have been announced before – that he says will see a Labour government achieve their goal within a Parliamentary term of five years.
- A network of regional public banks
- Expanded trade union rights
- Public services free at the point of use
- Free buses for young people
- Free childcare
- Restoring funding for public libraries, leisure centres and parks
He will say: “Behind the concept of social mobility is the belief that poverty is OK as long as some people are given the opportunity to climb out of it, leaving the others behind.
“I reject that completely, and want to see a society with higher living standards for everyone as well as one in which nobody lacks the means to survive or has to choose between life’s essentials.
Mr McDonnell will add: “As chancellor in the next Labour government, I want you to judge me by how much we reduce poverty… how much we create a more equal society… by how much people’s lives change for the better.
“Because that is our number one goal.”
Conservative Party Chairman Brandon Lewis has dismissed the pledge, saying Labour’s plans for the economy “would lead to worse living standards”.
He added: “Just this week we have seen wages rise by their fastest in 11 years, giving people more money in their pockets, and record numbers of people getting the security of a wage.
“Thanks to (the Conservative’s) balanced approach, we’ve also cut taxes for 32 million people, taking millions of the lowest paid out of paying income tax altogether, and taken action to reduce the cost of living.”