Oxfam is to cut 125 jobs and close several offices in England in a bid to save money and improve efficiency.
The anti-poverty charity also announced it will concentrate its work in fewer countries as it aims to deliver aid "in the areas of the world where it is needed most".
The changes will have a major effect at the charity's headquarters in Oxford, where 110 jobs are set to be axed.
Losses are expected across several departments, including human resources, campaigns, policy, finance and business support.
Mark Goldring, Oxfam's chief executive, said: " It is imperative that we have an Oxfam which lives within its means and is relevant to 21st century needs.
"Advances in technology mean we no longer need as much support in head office.
"Instead, our resources will be focused in the regions where we carry out the majority of our work.
"This will mean we can deliver the most effective and efficient support to the millions of people who go to sleep hungry each night."
The charity said the reforms would allow it to balance its budget and reflected "a shift in the organisation's priorities", as it focuses on poorer countries and on promoting poor women's rights.
Jane Cotton, Oxfam's human resources director, said: "This is the start of a consultation process with staff.
"We will make every effort to keep the number of redundancies to a minimum and where possible we will redeploy people and help colleagues find work elsewhere if this is not practical."
The charity's income fell by £17.6 million to £367.9 million in the year to March 31.
Oxfam GB employs 5,300 people across the world and has more than 22,000 volunteers.