Votes at 16 and 17 will be extended to council elections under legislation approved by the Senedd.
The new law will also allow councils to adopt a different voting system, aimed at producing results that better match the parties people voted for.
Welsh Government minister Julie James said the law will "empower" local government.
But it was criticised by opposition politicians as a "missed opportunity".
The Local Government and Elections bill, which will become an act once it receives royal assent, extends the franchise for council elections to voters 16 and 17 years old, and foreign citizens.
It mirrors measures already taken for the 2021 Senedd elections - the next council elections are due the year after.
Currently councillors are elected under first-past-the-post system, but the law also allows councils to adopt the single transferrable vote if they wish.
The system, which requires voters to select candidates by preference, is used in Northern Ireland, the Republic of Ireland and in Scottish council elections.
The bill also allows councils the power to potentially act more freely through a "general power of competence", and powers to voluntarily merge.
Local government minister Julie James said the bill will "enable us to implement our proposals for strengthening and empowering local government in Wales".
"It will build resilient and renewed principal and community councils, providing them with better tools to work with each other and with us, their communities, and across all sectors to reconstruct Wales in the light of the coronavirus pandemic," she said.
Welsh Conservative Mark Isherwood accused Welsh ministers of "holding Wales back since 1999, swamping localism and thereby shackling social entrepreneurship and community innovation.
"This Bill, which could have driven the changes needed, has instead become a missed opportunity."
Plaid Cymru's Delyth Jewell said the move to extend the franchise was welcome.
"But I have to say that there's been an opportunity missed here too. There was an opportunity to change the culture of local government in so many ways, introducing more equality and to change the voting system at a national level."
A total of 39 Senedd members backed the bill, with 16 voting against.