Construction will begin on a Tesco store on the estate's Market Street early next year.
A spokesperson for the Duchy of Cornwall said Market Street will also contain independent shops, cafes and restaurants.
It's expected around 100 jobs will be created by the new Tesco store - and will have a footprint of 2,283sq m.
Sam Kirkness, Nansledan Development Manager at the Duchy of Cornwall, said: “We’re delighted to have secured Tesco as part of Market Street’s exciting and diverse retail offer and are hugely encouraged by the number of direct approaches so far from local established businesses, independents and start-ups, all interested in becoming part of a modern-day high street and lifestyle destination for North Cornwall.”