Executive director Winnie Byanyima promised to root out any wrongdoing at the charity and provide justice for anyone abused by its staff.
She apologised for the scandal which has seen the charity accused of concealing the findings of an inquiry into claims that staff used prostitutes while delivering aid in Haiti in 2011.
Ugandan-born Ms Byanyima said: “What happened in Haiti and afterwards is a stain on Oxfam that will shame us for years, and rightly so. In my language: ‘Okuruga ahamutima gwangye, mutusaasire’ - it means ‘From the bottom of my heart I am asking for forgiveness’.”
The wide-ranging reform plan, which includes an independent commission involving women’s rights experts to urgently review to Oxfam’s culture and practices, has been agreed with Oxfam GB chief executive Mark Goldring.
Stating that “of course words are not enough”, Ms Byanyima went on: “Right now I have two utmost priorities for Oxfam: continuing to provide support to the millions of vulnerable people we work with around the world, and learning vital lessons from our past mistakes to make sure such abuse and exploitation does not happen again.”
The reforms include more than doubling the number of people working in Oxfam’s safeguarding processes while more than tripling the annual funding to £720,000.
They are also setting up a global database of accredited referees to ensure sex offenders cannot re-offend at other charities, and improving the organisation’s “whistleblowing mechanism”.
Oxfam also vowed to publish its 2011 internal investigation into staff involved in sexual and other misconduct in Haiti as soon as possible. The names of the men involved have already been shared with the authorities in Haiti.
Mr Goldring, who is to implement the changes in the UK, said the scandal has shown that Oxfam has “betrayed” the much-needed trust that people have put into the organisation.
He said: “What happened was a disgrace and we are absolutely committed to rooting out abuse across the organisation. We are doubling the number of people who work on safeguarding to make sure we are living up to our responsibility to protect staff, volunteers and the communities we support around the world.
“An independent commission is being established which will review our entire operations and tell us what we need to change about our culture and practices.
“It’s vital that we act to prevent those guilty of gross misconduct from simply moving on to another organisation and potentially harming other vulnerable people.
“Within Oxfam, we’re are urgently setting up a new database of people authorised to give references with an immediate freeze on references until that is in place.”
The announcement comes after the International Development Secretary met law enforcement chiefs on Thursday to discuss how vulnerable people receiving charity aid can be protected from sex abuse.
Penny Mordaunt held talks with Lynne Owens, director-general of the National Crime Agency, and Home Office officials.
They discussed how to “protect vulnerable people” and how to guarantee that “appropriate safeguarding provisions” are in place for charities involved in overseas aid, according to the National Crime Agency.
The Charity Commission also set out the scope of its statutory inquiry, which will probe the charity’s case records, its handling of the Haiti allegations and the extent of knowledge of similar allegations against staff in areas such as Chad and Liberia which pre-date Haiti.
The inquiry will also look at the charity’s communications with police and other agencies.