Four Enterprise trains which operate between Belfast and Dublin are to be refurbished at a cost of £12m, it has been announced.
The trains will have improved interiors, better access and a new booking system in a move aimed at improving the overall service for passengers.
The multi-million pound investment will mean that people travelling to and from the Republic will be able to do so in improved comfort.
The upgrade is expected to begin later this year using money which was originally earmarked for the Narrow Water bridge project in Warrenpoint, Co Down.
The trains, which are over 16 years old, have not enjoyed the same injection of funding as local services.
Over the past two years 20 new trains have been built, with some train stations also upgraded in Northern Ireland.
Regional Development Minister Danny Kennedy said his department is in the final stages of signing off the money.
He said: "I'm very pleased that we're in the final stages of crossing the Ts and dotting the Is of this particular project.
"It will mean a complete internal refurb for the Enterprise service. It will improve the travelling facilities for the increasing number of passengers who use it."
Most of the funding for the project is set to come from Europe, having been directed from the failed Narrow Water bridge project.
However, Translink and Irish rail operator Iarnrod Eireann is putting up some money for the upgrade.
It is hoped the project will allow the current service to continue for the next 10 years.
Translink chief executive Catherine Mason believes that the upgrade will "attract new people" to the route.
She said: "We anticipate a substantial passenger growth on the back of it and we have a lot of people who already use the service regularly, and we believe that this will attract new people.
"Much as our other enhancements have attracted people to the service, so we imagine that it will grow quite substantially."
Figures published last month showed that the number of passenger journeys on trains here rose to almost 13m in 2013, the highest in decades.
The number of people using trains has grown by 21% since 2009.