They are part of a joint venture portfolio the real investment trust holds with British Airways Pension Trustees Limited.
The joint venture has a 51% interest in the assets, which are the freeholds to 26 Sainsbury's supermarkets, while the grocer owns the remaining 49%.
The acquisition will be completed in March 2023 when the current leases expire.
The purchase price will be based on the assumption of a new 20-year lease to Sainsbury's with the initial rent set at the higher of passing or open market, subject to upward-only, five-yearly market rent reviews.
The supermarket chain can still buy another 10 stores in the portfolio. The option can be exercised between December 2021 and January 2022.
"Sainsbury's decision to buy back these stores is further evidence of the strength of demand for grocery property in the UK and also demonstrates the balance sheet strength of the supermarket operators,” said Ben Green, director of Atrato Capital Limited (LSE:CAPD, FRA:C8D) which is the investment adviser to Supermarket Income REIT.
“The exercise of this first tranche of options is expected to generate a positive net asset value impact for Supermarket Income REIT."