"I have worked long & hard with Robert. He will do a great job!" posted the President on social media.
O'Brien has served in the George W. Bush, Obama and Trump administrations.
O'Brien is an attorney from Los Angeles who has served as a foreign policy adviser to several Republican presidential campaigns, handled a number of high-profile legal cases and previously served in several State Department positions, including as an alternative representative to the U.N. General Assembly in 2005.
While speaking to reporters on Tuesday, Trump praised O'Brien in particular, calling the hostage negotiator "fantastic".
This is a developing story.
O'Brien, U.S. Special Envoy Ambassador, centre, arrives at the district court where United States rapper A$AP Rocky is to appear on charges of assault, in Stockholm, Sweden, Tuesday July 30, 2019.
After Swerdlick assessed that Trump snap-chose O'Brien to help him deal with several pressing worldwide developments, he expressed his view that O'Brien's handling of the A$AP Rocky affair wasn't a real demonstration of his capabilities. O'Brien also coordinates with the interagency Hostage Recovery Fusion Cell on the development and implementation of US hostage recovery policy and strategy.
Mr O'Brien is a corporate lawyer in Los Angeles, former United Nations official and former official in the George W Bush administration who write a book in 2016 titled While America Slept: Restoring American Leadership to a World in Crisis.
From 2008 through 2011, O'Brien was a presidentially appointed member of a government committee that advises on issues related to the trafficking of antiquities and other cultural items.
"He understands the world for the risky place it is".