Iarnród Eireann has said that 65% of its InterCity fares are to increase under a new fare structure that will come into effect next month.
There will be a reduction to 29% of train fares and 7% of fares will see no change.
The new structure replaces the current wide variety of tickets on sale with just three options - a single, a day return, and an open return for use within 30 days of departure.
The new fare pricing structure will be distance-based, so the longer the journey, the more expensive the ticket.
All single fares will be cheaper than day return fares and all day return fares will be cheaper than open return fares.
Fares will also be graded based on the speed of the train. Fares on Express routes will be highest, followed by Economy 1 routes and then Economy 2.
The new fares are the maximum that customers can be charged at train stations, but it does not prevent Iarnrod Eireann from offering promotional discounted fares as well.
The National Transport Authority approved the new fare structure using distance-based pricing.
It said fare pricing based solely on revenue maximisation was deemed inappropriate for a publicly subsidised service.
In total, 143 fares have been increased, by amounts ranging from 0.63% to 13.33%.
There will be reductions in 66 fares, ranging from 0.79% to 29.41%.
For example, the single fare on the Dublin Heuston to Cork route has been reduced from €66 to €60.
A day return fare from Dublin Heuston to Waterford has increased from €27 to €29.50.