The upgrade will accommodate for speeds of 200 kilometres an hour in future.
Over €91 million is being spent on cutting rail journey times on the Dublin to Cork line by 8 to 10 minutes.
The government funding will be spent on line improvements.
The route services midlands passengers in stations Portlaoise and Portarlington.
The upgrade will also futureproof the route to accommodate 200 kilometres an hour speeds at a later stage.