Jolie, who has visited Syrian refugee camps and marked other milestones during the conflict, said Thursday:
"Today, as we enter the fourth year of the conflict in Syria, my appeal is to world leaders.
"You are mothers and fathers as well as the leaders of your nations.
"I ask you to imagine your children going through the horrors in Syria.
"To think of children who are not only refugees, but also orphans. Children whose small bodies are being torn apart by bombs, or the hundreds of thousands who are starving to death at this very moment.
"I appeal to you to find it in yourselves to act with unity, on behalf of us all, and spare the Syrian people another year of unbearable suffering.
"UN Security Council Resolution 2139 demands access for aid into besieged areas and calls for an end to the conflict. It is time to turn that Resolution from a piece of paper into a plan of action.
"The conflict in Syria may have slipped off the front pages, but it should not slip for a second from our consciences or from the international agenda.
"The hard truth is that there are people alive in Syria today who will die as the bombs keep falling and no aid comes. For them, the conflict in Syria is a death sentence.
"There are many other Syrians who will be injured or become refugees, and suffer physical and mental scars that will last a lifetime.
"I call on the UN Security Council Member States to set out a path forward in the Geneva negotiations, and to insist on the implementation of UN Security Council Resolution 2139, and full humanitarian access to all parts of Syria."