Following in the footsteps of movie stars such as Peter Ustinov and the late Audrey Hepburn, Ms Sarandon will lend her fame - and just a little glamour - to the cause of improving children's living standards around the world.
"I feel as if all of my public work has been leading me to this, and I'm proud to begin as a Unicef Special Representative," Ms Sarandon, 53, said at the launch of a special report on the state of the world's children at the agency's New York headquarters. "I know `my world will be rocked,' as the kids say, by the people I meet and the places I visit.
"My intent is to speak on behalf of those whose voices are less readily heard - children and women at risk.
"We can't go on with business as usual. I ask responsible adults in every walk of life to become a mother, in the large sense of the word. Become a mother to the children of the new millennium."
Ms Sarandon, who used her Academy Award-winning role as Sister Helen Prejean in the film Dead Man Walking to campaign against the death penalty, has three children, one by the Italian director and screenwriter Franco Amurri and two by her present companion, the actor and director Tim Robbins. She and her family live in New York.