The new scheme will build on existing employment support and work placements delivered by the Department for Work and Pensions.
It will work with private companies, with the government anticipating businesses would cover at least some of the wages for job placements.
The government has not given a figure for the cost of the scheme but it will be funded from existing budgets set out in the spending review earlier this year.
Full details will be set out in November’s Budget, when the chancellor sets out the government’s tax and spending plans.
Reeves is facing a difficult Budget, with economists warning tax rises or spending cuts will be needed for the chancellor to meet her self-imposed borrowing rules.
In her conference speech, the chancellor is expected to say: “I will never be satisfied while too many people’s potential is wasted, frozen out of employment, education, or training. There’s no defending it.
“It’s bad for business, bad for taxpayers, bad for our economy, and it scars people’s prospects throughout their lives.”
She will add: “Just as the last Labour government, with its new deal for young people, abolished long-term youth unemployment I can commit this government to nothing less than the abolition of long-term youth unemployment.”
The announcement was welcomed by the Federation of Small Businesses as “hugely important”.
The group’s policy chair, Tina McKenzie, said: “Reprioritising spending from employment programmes which aren’t working to this type of scheme is exactly the way to get much-needed bang for taxpayer cash.”
She added: “Key to getting the details right is making sure there is a backstop offer to those who are now over-25, particularly those with health challenges; that young people out of work for health reasons are not excluded through misguided double funding rules; and that small businesses are enabled to play a full role in the delivery of the scheme.”
However, there are questions over whether businesses facing pressures including increases in National Insurance Contributions and the National Minimum Wage would be able to take on large numbers of new workers.
The number of job vacancies in the UK has been falling, hitting their lowest level since the pandemic earlier this year.