Labour says it would give under-25s in England free bus travel in areas where local councils bring services back into public ownership as the party wants.
The £1.4bn policy would be paid for by cash from vehicle excise duty currently earmarked for building new roads.
Leader Jeremy Corbyn will say "young people deserve a break" as he launches the policy in Derby on Thursday.
The Conservatives said it was "another promise from Labour that they have no real ability to deliver".
The policy would also apply for bus services under councils who franchised them out.
Providing government funding to councils for free bus travel could help up to 13 million young people save as much as £1,000 a year, according to Labour.
The proposal only relates to young people in England because bus policy in Scotland and Wales is handled by those nations' respective parliaments.
However, the party said it had costed the proposal for the whole of the UK and it would be a decision for the devolved governments if they would follow suit.
In his speech, Mr Corbyn will say young people "tend to be in lower paid, more insecure work, and they spend a higher proportion of their income on travel".
"Giving them free bus travel will make a huge difference to their lives," he will add.
Most local bus services were run by council-owned companies until the 1980s when the market was opened up to private competition by the Conservative government.
Shadow transport secretary Andy McDonald will repeat Labour's pledge to return to municipal bus companies if it wins power.
"We'll encourage local authorities to take back control of their buses so they can provide a better and more sustainable service to young and old alike, wherever they live," he will say.
Bus fares in England have risen by an average of 2.9% each year between 2012 and 2017 - which is higher than the typical rate of inflation (2.3%), Department for Transport figures show.
The annual number of passenger journeys fell by 1.5%, or 70 million, in the year ending March 2017 compared with the previous 12 months.
Conservative transport minister Nusrat Ghani said: "Last election Labour promised to pay off student debt if elected and then admitted it would actually cost too much to do. Now they're bribing young people again with yet another empty promise."
The government is trialling railcards for 26-to-30-year-olds "to help with the cost of travel" but faced some criticism when only 10,000 were released on the launch date last month, equating to just one for every 500 of the eligible population.