The former Army Secretary is expected to take his oath on Tuesday (Picture: US Department of Defense).
The US Senate has voted to confirm Mark Esper as the United States' new Defense Secretary.
The post has been vacant for longer than ever before in the Pentagon's history, following the resignation of Jim Mattis late last year.
It is believed Mr Mattis resigned over President Donald Trump's decision to pull US troops out of Syria.
Mr Esper has been carrying out the role in an acting capacity since Patrick Shanahan resigned last month.
He spent 10 years on active duty in the US Army and fought in the First Gulf War.
Watch: Tim Cooper reports on the appointment of Mr Esper.
He also served in the National Guard and Army Reserve for 11 years.
After retiring from the military in 2007, Mr Esper went into politics, working as a senior policy advisor to former Senator Chuck Hagel.
He later became policy director for the House Armed Services Committee and national security advisor for Senate Majority Leader Bill Frist.
During George W Bush's administration, he served as the Deputy Assistant Secretary of Defense for Negotiations Policy at the Pentagon.
He has also worked as a commissioner on the US-China Economic and Security Review Commission.