Authentic Brands Group will acquire Reebok from Adidas for a total consideration of up to £1.78bn.
Adidas will share the majority of the cash proceeds from the sale with its shareholders.
The transaction is expected to close in the first quarter of 2022, subject to customary closing conditions.
Adidas first bought Reebok for a reported sum of £2.75 billion in 2006 in an acquisition that also included the Rockport, CCM Hockey and Greg Norman brands.