Professor Alexis Jay, who led the Rotherham abuse inquiry, is to be the new chairwoman of the inquiry into child sex abuse in England and Wales.
The appointment was announced by the home secretary after the resignation of judge Dame Lowell Goddard last week.
Prof Jay was already among the panel of advisers taking part in the independent investigation into claims made against public and private institutions.
She becomes the fourth head after the three previous chairwomen stood down.
Home Secretary Amber Rudd said: "The independent inquiry has a vital role to play in exposing the failure of public bodies and other major organisations to prevent systematic child sexual abuse.
"I'm delighted Professor Alexis Jay has agreed to chair the inquiry. She has a strong track record in uncovering the truth and I have no doubt she will run this independent inquiry with vigour, compassion and courage."
'Open for business'
Ms Rudd added that the government's commitment to the inquiry remained "undiminished".
Professor Jay, 67, led the independent inquiry into child sexual exploitation in Rotherham which found that at least 1,400 children were subjected to sexual exploitation in the town between 1997 and 2013.
Professor Jay said: "I am committed to ensuring this inquiry does everything it has set out to do and does so with pace, with confidence and with clarity.
"Be in no doubt - the inquiry is open for business and people are busier than ever working hard to increase momentum.
"The panel and I are determined to make progress on all parts of the inquiry's work, including speaking to victims and survivors."
The inquiry has been beset by difficulties since it was set up in July 2014 to investigate allegations made against local authorities, religious organisations, the armed forces and public and private institutions in England and Wales, as well as people in the public eye.
Justice Goddard, a New Zealand high court judge, was selected following the resignation of two previous chairwomen in 2014. Baroness Butler-Sloss, the former President of the High Court Family Division, and her replacement Dame Fiona Woolf, a leading lawyer, stood down over their links to establishment figures.
In her resignation letter, Justice Goddard said conducting such a widespread inquiry was "not an easy task" but "compounding the many difficulties was its legacy of failure which has been very hard to shake off".
Who is Alexis Jay?
- Born in Edinburgh and educated at the Moray House School of Education, now part of the University of Edinburgh
- Led the Rotherham abuse inquiry, which concluded in August 2014 that 1,400 children in the South Yorkshire town had been subjected to sexual abuse
- Former chief social worker to the Scottish government and spent more than 30 years working in local councils in deprived areas of Edinburgh and Glasgow
- Visiting professor at Strathclyde University, where she chairs the Centre for Excellence for Looked After Children in Scotland
- In 2015 received an honorary doctorate from the same university
- Awarded an OBE in the 2012 Birthday Honours List for services to children and families
Prof Jay, who has worked in local government for 30 years, is the first of the chairwomen who is not a lawyer.
BBC legal correspondent Clive Coleman said Prof Jay was regarded as having done a "very fine job" of leading the Rotherham abuse inquiry.
But he said questions would inevitably be asked about her lack of judicial experience as she oversees a "mammoth inquiry" that will require her to exercise quasi-judicial powers.
Our correspondent added that many legal experts consider the inquiry to be too large, with some saying it will take 10 years or more to complete.
Labour MP Keith Vaz, chairman of the Home Affairs select committee, said Prof Jay was "clearly a suitable candidate with vast experience" but he said the public still needed a "full explanation" as to why Justice Goddard resigned.
Sarah Champion, Labour's shadow minister for preventing abuse and domestic violence, said Prof Jay was an "honest and fearless woman" and called on her to "swiftly bring about investigations and changes in practice so that more is done to prevent these horrific crimes".
Abuse inquiry: How we got here
7 July 2014 - government announces independent inquiry into the way public bodies investigated and handled child sex abuse claims. Baroness Butler-Sloss chosen as head
9 July - Baroness Butler-Sloss faces calls to quit because her late brother, Sir Michael Havers, was attorney general in the 1980s
14 July - she stands down, saying she is "not the right person" for the job
5 September - Lord Mayor of London Fiona Woolf named the new head of the inquiry
11 October - Mrs Woolf discloses she had five dinners with Lord Brittan from 2008-12
22 October - abuse victim launches legal challenge against Mrs Woolf leading the inquiry, amid growing calls for her resignation
4 February 2015 - Justice Lowell Goddard, a serving judge of the High Court of New Zealand, announced as the new head of the inquiry
13 July - Dame Lowell's pay is revealed as more than £480,000 a year
November - inquiry begins hearing directly from victims and survivors
4 August 2016 - Dame Lowell writes to Home Secretary Amber Rudd to resign from her post
11 August 2016 - Prof Alexis Jay announced as new head of the inquiry