"I am ashamed that this happened on my watch and I take full responsibility," she added.
Lawrence issued her statement as Oxfam executives were responding to a demand for full information from the British government's Department for International Development (DFID) which has threatened to cancel its multi-million dollar funding package.
"It is now clear that these allegations, involving the use of prostitutes and which related to behaviour of both the Country Director and members of his team in Chad, were raised before he moved to Haiti.
"I am desperately sorry for the harm and distress that this has caused to Oxfam's supporters, the wider development sector and most of all the vulnerable people who trusted us," she said.
Mark Goldring, Chief Executive of Oxfam GB, said: "I deeply respect Penny's decision to accept personal responsibility. Like us, she is appalled at what happened and is determined to do what is best for Oxfam and the people we exist to help."
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)