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.
Bahrain, Kuwait, Jordan face renewed Iranian attacks after US hits Iran's south
US forces bombed targets in southern Iran overnight after President Donald Trump said Tehran would pay dearly for the deaths of American soldiers, while Iran targeted US sites in Bahrain, Kuwait and Jordan and a tanker was hit in the Strait of Hormuz.
Lebanese army enters southern town after Israeli withdrawal, in first test of US-brokered deal
Lebanese army troops began deploying in the southern Lebanese town of Zawtar al-Gharbiyeh on Tuesday after Israeli forces withdrew from the area, a senior Lebanese security official said, in line with a US-brokered plan.
Kuwait lodges formal protest with Iran over tanker attack; ministry says power station fires contained
Kuwait's Ministry of Foreign Affairs today summoned Iranian Ambassador Mohammad Totonchi to deliver a formal protest note over Iran's targeting of the Kuwaiti tanker Kaifan in the Strait of Hormuz on Monday evening, which resulted in injuries to several crew members.
Russian attack kills three in Ukraine's Zaporizhzhia, officials say
A Russian guided-bomb attack on the southern Ukrainian city of Zaporizhzhia killed at least three people on Tuesday and injured more than a dozen, regional officials said.
French parliament backs social media ban for children under 15
French lawmakers approved on Tuesday a ban on social media access for children under the age of 15, as concerns grow around the world over the impact social media have on the health and safety of minors.
