The Sligo Town Centre development will cost €80m and will have 260,000 square feet of retail space, with Debenhams as one of the main stores.
Tesco, Penneys and Dunnes Stores, which are already in Sligo town, are planning to move into the new development.
Treasury Holdings say that 350 people will be employed during the construction of the centre.
It says a further 500 direct and indirect jobs will be created when it is completed, with Debenhams employing up to 120 of them.
Niall Kavanagh of Treasury Holdings said Debenhams will help to attract 'other big names to the development'.
'The deal makes the scheme real in what is a very difficult environment for delivering new developments,' he said.
'This is great news for Sligo and comes at the end of a lot of hard work from both sides over a 12-month period.'
