Lagan Construction is set to build and fit out the new Tesco Extra store at The Outlet, Banbridge.
The company's building team said up to 200 people will work on the project to build a 60,000 sq ft store, with 650 free car park spaces.
Works will include concrete piling, steel/timber frame structure, composite cladding panels, glazed curtain walling system and stone and timber external features.
Lagan Building Team said it was "delighted" to have secured the work – its first Tesco contract.
Director Tom O'Hare said: "The Lagan building team are delighted to have secured our first Tesco contract and look forward to working with Tesco and their entire team.
"Our dedicated team are fully committed to delivering a world-class service for our client."
There will also be a customer cafe, bakery, deli, phone shop, electrical shop, community room and staff areas. Lagan Building is registered with the Considerate Constructors scheme.
Store development manager Bernard Owens said: "We look forward to working with Lagan on the construction of our new Banbridge Bridgewater store to deliver an outstanding store for our customers."
The supermarket giant had originally planned an 80,000 sq ft store on the site but was refused planning permission – before the green light was given by planners for the second store.