Brown Thomas is to take over two floors of House of Fraser at Dundrum Town Centre.
The new shop is expected to employ more than 400 people when it opens next year.
House of Fraser will stop trading in May, making way for the retailer.
The company said "despite our best efforts... we have been served notice by our landlords in Dundrum".
House of Fraser says Dundrum Town Centre has "agreed an alternative deal with Brown Thomas".
As a result, House of Fraser Dundrum will close within the next 3 months.
The company hopes many of its Dundrum employees will secure jobs with the new tenants.
The new Brown Thomas store will comprise of over 63,000 sq ft with a retail sales area of 45,000 sq ft.
Following a complete refit, the shop will open in the first half of 2021.
Donald McDonald, managing director of Brown Thomas Arnotts said:
“We have been looking for a larger space at Dundrum for a number of years to enable us to deliver a more enhanced customer experience, and, in particular, to help grow our successful BT2 business there.
"In the meantime, it will be business as usual for the existing BT2 store in Dundrum, and for customers and team members.”
It's understood Penneys is in talks to take over the remainder of the space currently occupied by House of Fraser.