World Hunger Relief launched in 2007 and encourages Yum! Brands employees to raise money or volunteer for hunger relief activities.
Aguilera will appear on in-store advertising, public service announcements and will also be the face of FromHungerToHope.com with the aim to encourage people to give their time and money to charity.
David Novak, chairman and chief executive of Yum! Brands, said: "Christina's global iconic status will raise tremendous attention to this critical issue, and more importantly, will save millions of lives.
"We are extremely excited about Christina’s passion to join the fight against hunger."
Yum! Brands -- which also owns KFC and Taco Bell -- claims that one million of its employees, franchisees and their families have so far volunteered more than nine million hours to aid hunger relief efforts, and the program has raised $36m (£22m) for organisations such as the United Nations World Food Programme.
On its website Yum! Brands pledges to use its marketing clout to generate awareness of the hunger problem and convince others to become part of the solution.