Electric Ireland is to increase its residential electricity prices by 9% and residential gas prices by 7.8% from August 1.
The company said the increase is due to more expensive wholesale energy costs.
Electric Ireland last increased its prices in autumn when it raised electricity prices by 3.4%.
The increase announced today will add almost €100 a year to the average annual electricity bill and €60 to the average annual gas bill.
In April, almost all the country's energy suppliers increased their prices and in recent weeks Flogas, Pinergy, Panda Power and Iberdrola raised their prices for the second time this year.
Electricity prices in Ireland are already 23% above the EU average and the fourth most expensive in the 27-nation EU, recent figures from Eurostat show.
Gas prices here are the seventh most expensive in the EU.
Marguerite Sayers, executive director at Electric Ireland, said the company had hoped that wholesale prices might stabilise but unfortunately, they have continued to increase and are significantly higher than this time last year.
"As a result, we must reluctantly pass on some of these costs to our customers from August 1," she said.
Marguerite Sayers said the company appreciated this may be a difficult time for some customers, adding that it is committed to helping customers who are experiencing financial difficulty.
"We encourage any customers experiencing trouble paying bills to engage with us and we will commit to putting in place an affordable and workable payment plan with them in the coming months," she added.
Electric Ireland said it also continues to offer a 5% discount to customers experiencing financial hardship, through industry prepayment meters and the Household Budget Scheme.
Daragh Cassidy, Head of Communications at bonkers.ie, said today's news was almost inevitable given all the recent price increases that we have seen.
The cost of electricity in particular on the wholesale market has almost trebled since July of last year so these increases were bound to be passed on.
A lot of the country's electricity still comes from burning coal and gas in particular and while the price of these fossil fuels collapsed at the height of the pandemic, they have increased significantly in recent months as the world economy opens back up.
"What's more, transmission and distribution network charges - or more simply the charges for maintaining and running the country’s gas and electricity networks - were increased by the energy regulator late last year," Daragh Cassidy said.
"These charges make up around 30% of the price we pay for our energy and the increases have been passed on to customers," he added.