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.
Hong Kong court finds tycoon Jimmy Lai guilty in landmark security trial
Hong Kong's High Court on Monday found pro-democracy campaigner Jimmy Lai guilty of conspiracy to collude with foreign forces and to publish seditious material under a China-imposed national security law that could see him jailed for life.
Ukraine peace talks stretch into second day at start of pivotal week for Europe
Ukrainian President Volodymyr Zelenskyy will resume talks with US President Donald Trump's envoys in Berlin on Monday, after the US side said a "lot of progress" had been made on ending Europe's deadliest conflict since World War II.
Flash floods kill at least 37 people in Morocco's Safi province
At least 37 people have been killed in flash floods triggered by torrential rains in Morocco's Atlantic coastal province of Safi, Moroccan authorities said on Monday.
'Hero' who disarmed Bondi gunman recovering after surgery, family says
A Sydney resident who wrestled a gun from one of the alleged attackers during the mass shooting at Bondi Beach is recovering in hospital after undergoing surgery for bullet wounds to his arm and hand, his family said.
School bus accident in Colombia kills 17, injures 20
Seventeen people were killed and 20 injured after a bus carrying school children fell off a cliff in a rural area in northern Colombia, the local governor said on Sunday night.
Dubai is introducing a new front licence plate for motorcycles and e-bikes used in corporate delivery services. These vehicles previously carried only rear plates.
UAE President His Highness Sheikh Mohamed bin Zayed Al Nahyan has held a phone call with the President of the European Commission, Ursula von der Leyen, to discuss ways to strengthen ties in support of shared interests.
UAE President His Highness Sheikh Mohamed bin Zayed Al Nahyan has discussed enhancing cooperation with Niko Christodoulides, President of Cyprus, as part of the Comprehensive Strategic Partnership between the two nations.
