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.
Father, stepmother convicted of 10-year-old girl's murder after UK trial
The father and stepmother of Sara Sharif, a 10-year-old girl who was found dead in her home in Britain, were on Wednesday convicted of her murder after a trial which heard harrowing details of her treatment before her death.
Afghan Taliban's refugees minister killed in Kabul blast
The Afghan Taliban's acting minister for refugees, Khalil Rahman Haqqani, and six other people were killed in an explosion in the capital Kabul on Wednesday, his nephew said.
At least 33 dead after Israeli strikes in Gaza
Israeli strikes in the northern and central Gaza Strip on Wednesday killed at least 33 Palestinians, most of them in Beit Lahiya town in the north of the enclave, medics said.
Turkish-backed rebels take control of Syria's Deir ez-Zur
Syrian rebels backed by Turkey, who ousted president Bashar al-Assad, said on Tuesday they had taken the eastern city of Deir ez-Zur, while a war monitor confirmed Kurdish forces had withdrawn.
Death toll from missile attack on Ukraine's Zaporizhzhia rises to six
The death toll from a Russian missile strike that destroyed a clinic in the Ukrainian city of Zaporizhzhia on Tuesday has risen to six, while four more people remain under the rubble, the regional governor and emergency services said on Wednesday.
