New figures from the National Transport Authority (NTA) show 269 million journeys were taken on public transport last year.
That is an increase of almost 19 million, or 7.5%, compared to 2017.
The journeys were provided by Dublin Bus, Bus Éireann, Iarnród Éireann, Luas and Go-Ahead Ireland.
With a jump of 12.9%, Bus Éireann posted the single biggest percentage increase of any operator.
The company provided 35.1 million journeys in 2018, compared to 31.1 million in 2017 and 32.1 million in 2016.
Numbers on Bus Éireann's city services in Cork, Galway, Limerick and Waterford also grew by 13.2% overall.
Dublin Bus had the largest number of passenger journeys, at over 143 million - an increase of almost seven million on 2017.
The company has posted five straight years of passenger growth.
Iarnród Éireann saw DART and commuter services increase by between 4% and 5%.
Source: NTA
It also says the expansion of services through the Phoenix Park Tunnel and the introduction of the 10-minute DART schedule helped passenger numbers to expand.
The performance of intercity services grew from 11.4 million to 12.4 million.
Numbers on Luas increased by 11% to almost 42 million last year.
The Green Line extension to Broombridge, which opened in December 2017, and longer trams were among the factors.
Anne Graham is CEO of the NTA: "These numbers are very positive and are a testament to the range and quality of services provided by our public transport operators.
"It is clear that when there is a reliable, high quality, value-for-money public transport offering that customers will respond positively to it.
"But none of us can rest on our laurels, and the priority now must be to deliver on those improvements in our public transport infrastructure that are provided for under the National Development Plan announced last year."
The NTA says it plans to purchase more buses for use around the country, and will be moving to purchasing low-emission vehicles from July.
It is also looking to increase capacity on rail service by acquiring additional fleets in the coming years.
Meanwhile, work on extending current Luas trams to 55 metres is continuing.
