The four companies are phasing out their own loyalty schemes and will transfer them to Nectar, run by Keith Mills, the founder of Air Miles.
Mills has assembled an agency line-up of WCRS, Starcom Motive and WWAV Rapp Collins to launch a rewards scheme to rival Air Miles. Loyalty Management International, the company headed by Mills, will operate the loyalty programme for the companies, who are expected to be joined by Argos.
Nectar, which launches in the autumn, is the first loyalty scheme to be backed by multiple companies. Consumers with a loyalty card will be able to collect points when they buy through the four companies. The points can be redeemed with reward partners to be announced by Nectar in July.
These will include airlines, hotel and restaurant chains.
The involvement in Nectar marks Debenhams' first commitment to a loyalty scheme. The existing programmes operated by the other three companies have more than 12 million customers.
WCRS and WWAV Rapp Collins were appointed in March to work on the launch of Nectar, previously known as Project Mountain. It is expected to be backed by a £10 million launch advertising campaign and a large below-the-line spend. The Nectar brand identity was created by Corporate Edge.
Sir Peter Davis, the chief executive of Sainsbury's, said: "We think our customers will welcome and value the benefits that Nectar offers. It gives Sainsbury's a powerful tool with which to reward our existing customers and attract new ones."