Dr Michael McBride is beginning work as the new chief executive of Belfast Health Trust on Monday.
Dr McBride will combine the temporary role with his current position as chief medical officer.
Among Dr McBride's responsibilities as chief executive will be to improve unscheduled care services and elective care,
He will also lead the development of a new 10-year strategy for the trust.
Announcing the appointment of Dr McBride last month, Health Minister Jim Wells said he was a natural leader and gifted strategist.
"He has been at the forefront of medicine in Northern Ireland for two decades both as an accomplished physician and a highly respected government advisor," he said.
"He possesses all the skills and the wealth of experience required to lead Northern Ireland's largest provider of health and social care services."
The previous chief executive of the trust, Colm Donaghy, resigned in March of this year to become chief executive of Sussex Partnership NHS Foundation Trust.
In July, Bill Maher, the chief executive of the West/North West Hospitals Group in the Republic of Ireland, was offered the top job in the Belfast Trust but turned it down.