"When I learned that one in seven kids around the world go to bed hungry each night, I jumped at the chance to get involved," said Ronaldo.
"As a dad, I know it is important to give my two-year-old son a healthy life, right from the start, and I want to give all kids that same chance," he added.
Stating that it was an honour to join 'Save the Children', Ronaldo said, "I want to work with them to make sure that fewer parents will have to struggle with putting the right kinds of food on the table. I also want to encourage kids to get out there, get active and get fit."
The Portugese captain said he will in the footsteps of Save the Children artist ambassadors -- Jennifer Connelly and Julianne Moore -- in lending his voice and visibility for good.
"We are delighted to have such an incredible athlete working with us. Many children around the globe look up to Cristiano as a role model for healthy living and keeping fit," said Thomas Chandy, CEO of Save the Children.
Shabana Azmi, Parineeti Chopra and Kunal Kapoor are among Save the Children's ambassadors from India.
Last year, Save the Children reached more than 85 million children in nearly 120 countries with programs that help the kids survive and thrive, and reach their potential.