Shelley joined Tesco in May 2012 from her role as a partner at the agency Brunswick, where according to LinkedIn she had spent nearly five years, having previously been group comms director at the insurance firm Prudential.
Shelley said in a statement issued by Tesco this morning that she planned to "take a short break before exploring new opportunities in both executive and non-executive positions".
In May, PRWeek reported that Tesco had been in discussion with potential candidates to replace Shelley, as it struggled to deal with the fallout from an accounting scandal and declining revenues – although Tesco denied that this was the case.
Tesco's statement this morning said Shelley had "helped to ensure Tesco's narrative and turnaround plans were communicated consistently and clearly both internally and externally, which was particularly challenging given the significant changes facing the business" - and that a search for her successor "is now underway".
Dave Lewis, Tesco chief executive, said: "I am extremely grateful to Rebecca for the support and counsel she has given me since I joined Tesco. Since joining the business, Rebecca has led the group communications team with distinction at a time of great change for Tesco. I know her colleagues on our executive committee and in her own team will miss her energy and good humour. I’d like to wish her every success for the future."