'We are going to talk about things differently,' said director of corporate communications Julie Wood. 'Instead of focusing on Oxfam's work, we're going to say that, working together with Oxfam, people really can change the world.'
Oxfam will champion everyday heroes who raise money and get involved in the development charity, showing how ordinary people can make a difference.
Wood said focusing on the world's problems can make people feel useless and creates a 'sense of apathy' among the public.
Instead, Oxfam will start telling more good news stories, focused on solutions.
'You don't hear that the number of people living in poverty on less than $1 a day is going down,' she said.
Oxfam's new strapline 'Be Humankind' will be used in a series of new adverts.
Meanwhile, Oxfam is to relaunch its stores at an event on 7 May. The stores will be open to the public on 10 May.
Oxfam has just handed another six-month contract to fashion specialist Devetta PR, which it brought in last November to supervise the relaunch of the stores.
The charity will stress the stores' ethical credentials, positioning them as sustainable fashion boutiques.
Devetta will target national newspapers, the fashion press, glossy magazines and the style sections. Founder Philippa Devetta will lead the pro bono account.
Former Topshop brand director Jane Shepherdson is also involved in the launch. She has been working with the charity on a voluntary basis as a creative consultant.