Dunnes has overtaken Tesco as the second biggest retailer by supermarket share here, according to the latest figures from Kantar Worldpanel.
In the 12 week period to October 9, sales at the retailer grew by over 6%, bringing its share to 22% of the grocery retail market.
Performance at Tesco improved compared to previous months, with sales values falling by just 1.3%.
That was the lowest level of decline since May of this year.
Sales volumes increased in the period.
SuperValu's share of the market dropped marginally to 22.4%, but it retains its position as the biggest retailer by supermarket share.
It recorded sales growth of almost 3% in the period and it managed to recruit an additional 38,000 shoppers during the past 12 weeks compared with last year.
"The biggest factor driving growth for Dunnes over the past year has been an increase in the size of the average shopping trip, which has grown by €3 to €38.10.
"The retailer with the next largest trip size is Aldi, where shoppers part with €25.10 on average - €13 less than at Dunnes," David Berry, director at Kantar Worldpanel, explained.