From the end of this month, each customer will earn two Nectar points for every £1 spent across the chains' combined 400-restaurant portfolio.
The launch will be supported by point-of-sale activity and a campaign to promote the family-oriented restaurants ahead of the school summer holidays.
Although this is Nectar's first full sponsor in the dining sector, the two brands were already reward redemption partners, along with McDonald's and TGI Friday.
Nectar sponsors are guaranteed exclusivity in their sectors. However, dining is not closed to additional partners, and Nectar's parent firm, Loyalty Management UK, said it was seeking a takeaway and a fast-food sponsor. A McDonald's spokeswoman said it had no plans to extend its partnership.
Details of Brewers Fayre and Brewsters' involvement will be included in Nectar's mailing to cardholders in September.