A new express train service would cut journey times from Cardiff to London by 20 minutes if it is given the go-ahead.
The proposed open-access service by Grand Union Trains would run alongside current Great Western Railway trains to Paddington station.
Operating on the south Wales mainline, the service would stop at less stations on the journey, making it quicker.
The Office of Rail and Road (ORR) said it was aware of the proposal and early talks had started.
The hourly service would operate between London Paddington and Cardiff Central and could be live by December 2020.
It would stop at Severn Tunnel Junction in Monmouthshire, a station which is not currently served by Great Western’s London service.
Grand Union said their service would take one and a half hours – by not stopping at Swindon, Didcot and Reading – in comparison to Great Western’s half-hourly service, which takes more than two hours.
The firm’s managing director Ian Yeowart said: “The trains we offer will be faster, more comfortable, we’ll offer some competition so that will have a downward pressure on price.
“We look for places that deserve a better rail service and can support a better rail service.”
Mr Yeowart said he has also been in talks with the Welsh Government about other improvements to rail services.
“We’re not just talking about trains, we’re also talking about potential infrastructure at Severn Tunnel Junction and a Cardiff Central Station so there’s a lot of exciting things to happen,” he added.
“We also plan to base the entire operation in south Wales so there would be about 135 new jobs to come into the area if we’re successful.”
They propose using second-hand 140mph (225 km/h) trains formed of nine coaches and a driving trailer, which have been used by London and North Eastern Railway on the East Coast Main Line.
Grand Union has previously launched open-access passenger services for Grand Central between London King’s Cross and Sunderland and King’s Cross and Bradford.
Prof Stuart Cole, a former director of Wales Transport Research Centre at the University of Glamorgan, said Mr Yeowart had a “proven record” in this field.
“He’s been in this business before, last time it was very successful,” he said.
“He’s gone for the most profitable and busiest part of the line, it’s extra trains on the market and we can see what prices come to the market.”
Under track access rules, other rail operators are able to provide a service if a route is not deemed congested, and the Office of Rail and Road (ORR) approves an application.