Ikea has formally lodged a planning application for a 29,000 sq m store to be built on the outskirts of east Belfast.
The site is near the newly renamed George Best Belfast City Airport.
If approved, the store will open early next year, with the planned Dublin store opening its doors within a few months.
The Belfast development is larger than was originally anticipated when the investment announcement was made in January.
Some 400 jobs will be created, with a further 100 jobs arising from what the company calls "out-sourced services".
The 14.5-acre Holywood Exchange site is linked by dual-carriageway to the North's two motorways, and is being developed to service the northern half of Ireland, a spokesman said.
Both the Belfast and Dublin stores would be "full-size and full-range", The Irish Times was told.
The increased scale of the Belfast investment reflected the company's confidence in the stability of the consumer market.
The company had hoped for the planning process to have been at a more advanced stage, but the new revised plans and tests associated with the Belfast site have slightly delayed the application.
It will consist of two levels of retail warehouse and parking area for 1,455 cars.
The store will incorporate a showroom, market hall and warehouse, as well as a 500-seat restaurant, creche, staff facilities, children's outdoor play area and customer services facilities.
It will carry 9,500 products and allows customers to view over 55 fully furnished layouts.
Theresa Daly, Ikea's project manager for both the Belfast and Dublin stores, said yesterday: "We believe that our application meets all of the tests of national policy as well as national and local planning guidelines."
A spokesman said the company was confident that issues relating to traffic management at the proposed Dublin store near the M50 would be met, and that the planning process would soon proceed.