The head of the Press Complaints Commission (PCC) has announced she will step down after criticism of its handling of the phone-hacking scandal.
Baroness Peta Buscombe has chaired the watchdog since April 2009 but has faced a backlash over the saga, which led to the closure of the News of the World.
Baroness Buscombe said she would not continue in the role when her three-year term in office ends next year.
She will aid the Leveson phone-hacking inquiry as a media regulation expert.
Baroness Buscombe said in a statement: "I am pleased that the commission want me to continue in post until my successor has been appointed.
"Thereafter, I will be able to be a campaigner for change from outside the organisation.
"I wish to contribute to the Leveson inquiry and participate fully in the overall debate regarding reform, unfettered by my role as chairman of the PCC."
Baroness Buscombe, 57, is a former lawyer and chief executive of the Advertising Association.
She was elevated to the House of Lords in 1998 and has been a Tory frontbench spokeswoman on several subjects.
In November 2009, she withstood calls to resign after she questioned lawyer Mark Lewis's evidence to MPs over phone-hacking allegations at the News of the World (NoW).
Mr Lewis brought a libel action against the PCC and Baroness Buscombe over the comments.
She also came under fire the same month for a report in which the PCC appeared to clear the NoW of phone hacking after after the paper's former royal editor Clive Goodman and investigator Glenn Mulcaire were jailed in 2007.
The PCC was established in 1991 to enforce a code of practice for UK newspaper and magazine publishers and editors.
Earlier this month, Prime Minister David Cameron accused the PCC of being "ineffective and lacking in rigour" and cited the need for a "new system entirely". Labour leader Ed Miliband said the self-regulatory body was a "toothless poodle".
The PCC said in a statement that Baroness Buscombe would leave the watchdog in a "better position to continue its evolution".
Lord Black of Brentwood, chairman of the Press Standards Board of Finance which funds the PCC and will appoint a new chairman, said: "Baroness Buscombe has given the PCC independent and strong leadership during the most turbulent and challenging time in its history.
"She has initiated a series of reviews and reforms which will strengthen the PCC and the services which it provides to the public.
"We thank her for her huge contribution in leading the PCC forward during the past two years and wish her well for the future."
On Twitter, former deputy prime minister John Prescott, wrote: "I'm glad Buscombe is going but she shouldn't be replaced with another puppet of the papers. We need major reform & a truly independent PCC."
The Media Standards Trust said her decision was "the right one".
"There has clearly been a failure of leadership at a time when the PCC needed firm direction," the charity said.
In other developments, the Commons culture, media and sport committee has voted not to recall News International chairman James Murdoch to give more evidence on phone hacking, after two ex-News of the World employees disputed Mr Murdoch's comments to the committee.
The committee will ask for more details about an email which is said to claim phone hacking was widespread across the now defunct newspaper, and chairman John Whittingdale said it was "very possible" Mr Murdoch would be asked to reappear after that.
Meanwhile BSkyB's board has unanimously agreed to keep James Murdoch as its chairman.