Angelina Jolie steps down as UN refugee envoy
"I believe in many things the UN does, particularly the lives it saves through emergency relief," Jolie, 47, said.
And she added: "I will be working now with organisations led by people most directly affected by conflict, that give the greatest voice to them."
The UNHCR said she was one of the most influential refugee rights advocates.
In a post on her Instagram page, the Hollywood star wrote: "After over 20 years, I am stepping down today from my work with the UN refugee agency.
"Refugees are the people I admire most in the world and I am dedicated to working with them for the rest of my life."
Jolie provided no details about the organisations she was planning to work with.
Meanwhile, the UNHCR said in a statement that Angelina Jolie would "engage on a broader set of humanitarian and human rights issues".
In a statement, the refugee agency said "Jolie has worked tirelessly, carrying out more than 60 field missions to bear witness to stories of suffering as well as hope and resilience".
Jolie - who starred in a number of blockbusters including Mr and Mrs Smith and Lara Croft: Tomb Raider - has worked with the UNHCR since 2001, becoming the agency's special envoy in 2012.
In recent months, she has met displaced people in the war-torn Ukraine, Yemen and also Burkina Faso.