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.
At least 9 killed in hotel fire in India's Kolkata
At least nine people have been killed, including a child, in a fire at a hotel in India's eastern city of Kolkata on Wednesday, local police said.
Ebola cases in Congo exceed 5,000, government data shows
The number of confirmed Ebola cases in the Democratic Republic of Congo now exceeds 5,000, government data has showed late on Tuesday, as health officials warn that response efforts are failing to contain the deadly disease.
8 Israeli airstrikes hit Syria's Abu al-Duhur airbase, state TV reports
Eight Israeli airstrikes have hit the Abu al-Duhur military airbase in northwestern Syria early on Tuesday, targeting the runway and storage facilities, Syria's state-run Ekhbariya said, citing a military source.
Indonesia earthquake death toll rises to 70, government aid arrives
The death toll from the powerful 7.7-magnitude quake that struck Indonesia last Saturday has risen to 70.
Two killed in high school shooting in southern Philippines
Two students were killed in a shooting at a high school in the southern Philippines on Tuesday, one of them the gunman, officials said, in the second such incident in the country in less than two months.
