Airtricity has confirmed its prices are going up from October 15 of this year.
The company has around 370,000 electricity and 110,000 gas customers.
It will increase electricity prices by 4.7% and gas by 8.5%. However, customers on pre-payment meters will not be affected.
Bord Gáis and Electric Ireland both recently announced similar increases from October 1.
Airtricity said that sustained and considerable increases in the costs of using the gas and electricity transmission and distribution networks regulated by the Commission for Energy Regulation, as well as the continued weakening of euro against sterling, have resulted in upward pressure on energy prices.
"We sincerely regret having to increase our prices at this time. In difficult economic conditions, increasing prices is one of the hardest decisions any business has to take,'' commented the company's managing director Stephen Wheeler.
''Unfortunately, however, factors outside of our control, such as the increase in gas and electricity pass through costs and the cost of the euro against sterling, mean that these price increases have become unavoidable,'' he added.