Full year sales at Primark and Penneys shops rose 15% to £3.5 billion (€4.4 billion) over the year to 15 September.
This is according to results published by parent company Associated British Food.
The low-cost fashion retailer opened 19 new shops during the year, added 10,000 new staff and saw its operating profit rise by 15% to £356m (€444m).
In a statement alongside the results, chief executive George Weston said that Primark's operating profit margin remained steady at just over 10%.
Higher cotton prices over the first half of the year, offset by a fall in prices over the past six months, boosted profit for the company.
Penneys is in the process of expanding its flagship Mary's Street shop in Dublin, which was the retailer's first outlet. The revamp is expected to be completed early next year.
Primark began trading in Ireland as Penneys in 1969 and currently has 38 Irish outlets. Primark operates 249 stores in total in the UK, Ireland, Spain and five other European countries.