It follows reports that President Trump was outraged by comments made by Mulvaney during the Ukraine corruption saga.
The allegations of abuse of power over the Ukraine incident led to impeachment proceedings against President Trump.
Mulvaney's departure has been on the cards for the last few weeks.
Mr Mulvaney is to become US special envoy to Northern Ireland, while North Carolina lawmaker Mark Meadows has been appointed to take over his former position.
US considering 'winding down' military efforts in Iran, says Trump
President Donald Trump said on Friday the US was getting very close to meeting its objectives as it considers winding down its military efforts in the Iran war and called on countries that use the Strait of Hormuz to guard and police it "as necessary".
Fire at Korean car parts factory kills 14, injures 60
Fourteen people died and 25 were seriously injured in a fire at a car parts factory in the South Korean city of Daejeon, fire authorities said on Saturday.
Trump's peace board hands Hamas disarmament proposal, sources say
Donald Trump's Board of Peace has presented Hamas with a written proposal on how it could lay down its weapons, two sources said, a step the group has thus far refused to take as the US president pushes on with his plan for Gaza's future.
Iran ready to let Japanese vessels transit Hormuz, Kyodo reports
Iran is ready to let Japanese-related vessels pass through the Strait of Hormuz, a vital artery for global oil supplies, Kyodo news has reported, citing Iranian Foreign Minister Abbas Araqchi.
Putin tells Tehran: Russia stands by Iran
Russian President Vladimir Putin has congratulated Iranian leaders on Nowruz and said Moscow remained a loyal friend and reliable partner to Tehran, the Kremlin said on Saturday.
