A twelve-month trial will assess the level of demand for more services
Arriva Cross Country has promised to more than triple the number of trains serving Chepstow station from May.
Ten trains a day will stop at Chepstow on each direction of the Cardiff to Nottingham route Mondays to Saturdays.
Currently, only two trains a day stop there on the northbound service and three a day on the return run.
"This is excellent news for rail passengers," said a spokesperson for the South East Wales Transport Alliance (SEWTA) of local councils.
"With petrol prices at their highest levels ever, these extra services present a great opportunity for travellers to reassess their travel opportunities, and make better use of more sustainable alternatives," said the spokesperson.
Lydney station will see an increased daily service of six stops in each direction.
Ten reasons to stop at Chepstow
13th Century Port Wall
1816 Iron Bridge
Piercefield House and Park
Wyedean Forest Rally
Border Morris Dancing
Poetry at the Drill Hall
Offa's Dyke Path
Gateway to the Wye Valley
Arriva Cross Country said it had agreed to a 12-month trial of additional stops in response to appeals from local residents and interested parties.
Managing Director Andy Cooper said: "We are pleased to be introducing these trial services from May.
"Over the coming months we will work with local stakeholders and rail user groups to raise peoples' awareness of the new services at Chepstow and Lydney.
"We are told there is a pressing need for the more frequent service and we shall be delighted if this proves to be so."
Michael Greedy of the Passenger Focus watchdog organisation also welcomed the move.
"Passengers have been asking for more trains for a considerable period of time and it will now be up to them to prove that they will use the additional services on a regular basis," he said.
"This is a trial period and it will very much be a case of 'use it or lose it'.
"The future of a better rail service at these stations is firmly in passengers' hands."
Campaigners say trains could ease congestion on the A48 in Chepstow
The local campaign group Better Trains for Chepstow has also welcomed the trial.
Chair Jim Jenkins said: "The announcement is good news and came as a great surprise for we knew that the Welsh Assembly Government were seeking improvements but after many years of trying we didn't expect such success.
"Naturally we would like to have all the trains scheduled to stop at Chepstow to provide a regular and predictable pattern of service, our objective for the past 5 years.
"But we recognise that passenger growth at Lydney is as at least as great as Chepstow and by sharing the services as proposed the trial should provide valuable information to shape the services for the future.
"This is an example of the way that train service improvements are possible at little or no additional cost and makes refreshing news when all we hear about are cuts."