An extra 20 carriages will be added to the Welsh rail network by next year.
The new rolling stock is being leased following a £1.9 million investment by the Welsh Government and £1m from Arriva Trains Wales, and will allow existing rolling stock to be refurbished.
Economy and Infrastructure Secretary Ken Skates AM said: “I’ve made no secret of the difficulty in adding good quality rolling stock in Wales and am delighted that, by working with Arriva Trains Wales and others, we’ve been able to secure these extra trains.
“I’ve been absolutely clear that the next franchise, the Welsh Government’s first, must have the passenger at its heart. I’m delighted that we’ve been able to secure these trains and hope to see them play a part in boosting Wales’ rail service for years to come.”
Operator Arriva Trains Wales’ contract is due to end in 2018, and is one of four companies in the running to take on the Wales and Borders rail franchise.
Arriva has come in for criticism from commuters, with many claiming they are regularly left standing on overcrowded or delayed services.
Simon Hughes, Fleet Director for Arriva Trains Wales, said: “These additional trains will be a massive boost for our customers who have been calling for extra capacity for a long time.”