Miller was responsible for overseeing the retailer's business transformation programme.
Asda director of European strategy Angela Morrison will join Sainsbury's in February, and will replace Miller after a month handover.
'We would like to thank Maggie for the significant contribution to Sainsbury over the past four years and look forward to Angela joining in the New Year,' said a Sainsbury's spokeswoman.
Miller said that it's too early to announce where she is moving.
More details on this story will appear in the Technology section of next week's Retail Week