Dido Harding is to step down as chief executive of TalkTalk after seven years at the telecoms firm.
She will leave the position in May and be succeeded by the managing director of consumer, Tristia Harrison.
Ms Harding said: "After seven extraordinary and fulfilling years, during which we have transformed TalkTalk's customer experience and laid the foundations for long-term growth, I've decided it's time for me to start handing over the reins at TalkTalk and focus more on my activities in public service.
"I am very proud to be handing over to the next generation of TalkTalk leadership who, together with Charles, have played such an integral part in the success of the business to date.
"Between now and May, we will work together on a handover that maintains focus on this year's performance and enables the new team to prepare for the next financial year and beyond."
As part of a board shake-up, the group's founder Sir Charles Dunstone will step up from chairman to executive chairman.
He will relinquish his chairmanship of retailer Dixons Carphone as a result.
Charles Bligh, managing director of TalkTalk Business, will become chief operating officer.
TalkTalk was stung by a cyber attack in 2015 under Ms Harding's watch, which saw the personal data of nearly 160,000 people accessed by hackers.
The debacle was branded a ''car crash'' by the then information commissioner Christopher Graham, who said it should send a warning shot to the industry.
The attack led to tens of thousands of customers deserting the firm.
Sir Charles said: "Dido has been a tireless, energetic and effective force for good from the day she joined TalkTalk.
"As a result of her leadership and total commitment to all of us who work here and our customers, she has helped transform TalkTalk into a much stronger business."
Ms Harding's departure was announced alongside a third quarter trading update which saw group revenue fall from £459 million to £435 million, blamed on the impact of re‐contracting and re‐pricing legacy tariffs.