Electric buses are set to go into service in Cardiff and Caerphilly backed by £8.5m worth of UK government funding following trials last year.
Cardiff will have a fleet of 36 buses, while Stagecoach will have 16 for its Caerphilly depot.
The money comes from a £48m Department of Transport grant scheme to promote greener public transport across England and Wales.
Newport Transport is being awarded just under £1m to fund one electric bus.
Caro Wild, Cardiff Council's cabinet member for transport, said the grant aid would help support the city's clean air ambitions.
"People are excited about electric buses - they can see the health benefits," he told the Local Democracy Reporting Service.
"This announcement is pay-off for the hard work we've been putting in behind the scenes to try and maximise every opportunity we have to improve air quality in Cardiff."
Nigel Winter, managing director of Stagecoach South Wales, said the first single-decker e-buses would be running from its Caerphilly depot in 2020.
He said the new zero-emission vehicles would help to "significantly improve the customer experience" and encourage motorists to switch to a greener means of travel.
Mr Winter added that the firm was working with others to create an all-electric passenger transport network for Caerphilly, with new electric trains promised from 2021 as part of the South Wales Metro project.
Buses Minister Nusrat Ghani said the UK government was "doing more than ever before to reduce emissions across all modes of transport".
"I'm delighted to see the bus industry putting itself at the forefront of this," she said.