The 50-year-old, who only took over from previous Director General Mark Thompson on September 17, resigned by delivering a statement alongside head of the BBC Trust Lord Patten this evening (November 10).
Entwistle took the decision to resign after serious back-to-back scandals at the corporation involving child abuse - firstly, the revelation that a story alleging that Jimmy Savile was guilty of child abuse was quashed by a Newsnight editor, and that Newsnight had broadcast child abuse allegations that led to former senior Tory peer Lord McAlpine being falsely implicated.
He told journalists in a short statement: "In the light of the fact that the Director-General is also the Editor-in-Chief and ultimately responsible for all content; and in the light of the unacceptable journalistic standards of the Newsnight film broadcast on Friday 2nd November; I have decided that the honourable thing to do is to step down from the post of Director-General."
He concluded by saying: "While there is understandable public concern over a number of issues well covered in the media - which I'm confident will be addressed by the Review process - we must not lose sight of the fact that the BBC is full of people of the greatest talent and the highest integrity. That's what will continue to make it the finest broadcaster in the world."
Lord Patten said that the resignation marked "one of the saddest evenings of my public life", and added that Entwistle had "behaved extremely honourably and in the best standards of journalistic integrity".
Director of BBC Audio and Music Tim Davie has been named the acting Director-General, despite reports that he would take up the post of chief executive at BBC Worldwide next month.