M&S estimates the incident will cost approximately £300 million in lost profits, though it expects to recover up to half through various measures, and personal customer data was also stolen.
Hacking groups named DragonForce and Scattered Spider have been linked to the cyberattack.
Archie Norman, M&S's chair, described the cyberattack as "traumatic" and an "out-of-body experience," highlighting the significant effort required by staff to manage the disruption.