Freida Pinto, the actress best known for her role in Slumdog Millionaire, was so touched by a trip to Africa where she met some of the world's poorest girls that she has signed up as a charity ambassador.
Pinto has joined up with Plan International to champion its Because I Am A Girl (BIAAG) campaign.
Campaigners are pressing for international action on poverty-related obstacles and human rights abuses keeping millions of girls out of education.
Pinto said: "I've always been a true believer in the power of every individual, especially every girl. I had the amazing opportunity to travel with Plan to Sierra Leone to see first-hand how investing in a girl transforms an entire community."
The BIAAG campaign will be the centrepiece of the first International Day Of The Girl and aims to reach four million of the world's poorest girls and young women.
Marie Staunton, Plan's UK chief executive, said: "Girls and young women are often at the sharp end of many harrowing issues associated with global poverty and discrimination - whether they are victims of rape as a weapon of war or forced to offer sex in exchange for food for their survival.
"Child marriage, teen pregnancy, maternal mortality and limited access to education and family planning, are some of the grim issues that millions encounter.
"We are thrilled to have Freida Pinto as an ambassador of a campaign which aims to transform the lives of girls whose lives have been blighted as a result of their age and gender.
"We hope her support and our work with local communities will enable millions more girls to move from impoverished existences to lives with productive and progressive opportunities."