The former Army Officer was appointed just hours after Boris Johnson took the position as Prime Minister (Picture: Crown Copyright).
Former Army officer Ben Wallace has been appointed as Defence Secretary, replacing Penny Mordaunt.
Ms Mordaunt, herself a Royal Navy reservist, left her cabinet position after 85 days in post.
Speaking for the first time since the announcement, Mr Wallace said: "As a former officer with the Scots Guards, it is an honour to take up this role at the Ministry of Defence.
"I know first-hand the dedication and hard-work of our Armed Forces and I will be committed to ensuring their interests come first.
"I look forward to getting started and meeting colleagues from across the department and our military."
Mr Wallace was commissioned into the Scots Guards at 20 years of age and during the 1990s served in Northern Ireland, Germany, Cyprus and Central America. In 1992 he was mentioned in dispatches.
On his first day as Defence Secretary, Mr Wallace tweeted thanking his predecessor, Penny Mordaunt, saying he has "big shoes to fill".
"She is a wonderful colleague and did a great job at the MOD," he said.
He will also come into the job well briefed on at least some aspects of a complex job having served as Home Office Minister for Security and Economic Crime since 2016.
It is a job that includes responsibilities for implementing the strategic defence and security review and counter-terrorism.
He has also previously worked for defence contractor QinetiQ as their Overseas Director in the Security and Intelligence Division.
Ben Wallace has largely voted with other Conservative MPs since coming to Parliament but he has generally voted against same-sex marriage.
Confirming she was leaving cabinet, Penny Mordaunt posted on Twitter, saying: "I’m heading to the backbenches from where the PM will have my full support, as will my successors.
"Thank you to everyone who's helped me get things done, especially our Armed Forces and civilians in defence for the last 85 days.
"We achieved much."
Ms Mordaunt has also left her role as Minister for Women and Equalities.
I’m heading to the backbenches from where the PM will have my full support, as will my successors at @DefenceHQ & @WomenEqualities— Penny Mordaunt MP (@PennyMordaunt) July 24, 2019
Thank you to everyone who’s helped me get things done, especially our Armed Forces and civilians in defence for the last 85 days. We achieved much??
Penny Mordaunt was appointed as the first-ever female defence secretary in May, following Gavin Williamson's removal.
Meanwhile, Mr Williamson has also been appointed as Education Secretary.
He was sacked in May by then-Prime Minister Theresa May.