The four-day London conference is organised by British Foreign Secretary William Hague and Jolie, a United Nations special envoy.
They hope representatives of the more than 100 countries present will back a new protocol laying out how sexual violence in conflict zones should be investigated and prosecuted. They say they want to end the "culture of impunity" for wartime sex crimes.
Pitt watched from the audience as Jolie and Hague spoke to delegates at the east London conference venue.
Jolie said the meeting, which ends tomorrow, was being held "for all the forgotten, hidden survivors who have been made to feel ashamed or been abandoned."
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"And for the children of rape we want the whole world to hear their stories and understand that this injustice cannot be tolerated, and that sorrow and compassion are not enough," she said.
Hague and Jolie have made an odd but effective double act as they've campaigned against sexual violence for the past two years.
Governments like the one I am a member of hold in their hands levers of decision-making and action. And this combination can be formidable.