The planned work will appear at major UK music festivals, including Glastonbury, using a new strapline: "Live your life, change your world."
The agencies were appointed following a pitch that was called earlier this year, and will aim to attract young supporters to Oxfam and show them how they can get involved.
The winning pitch idea was based around the strategy that people can still do what they love doing, while changing the world. The presence at festivals will be supported by a 60-second ad, print ads, information booklets and a website, oxfam.org.uk/generationwhy.
Julie Wood, the director of corporate communications at Oxfam, said: "We are excited about the new campaign and feel confident it will engage a young audience with Oxfam in a relevant way."
Separately, Oxfam is looking to appoint an ad agency to develop a pre-Christmas fundraising campaign. It is also reviewing its media planning and buying.