The 46-year-old who previously served as international development secretary, was a prominent face in the campaign to leave the European Union (EU).
She has become the first woman to hold the position of defence secretary position after Gavin Williamson was sacked over a leak about a National Security Council meeting on Chinese tech giant Huawei's potential involvement in the UK's 5G network.
She also retains the job of minister for women and equalities.
The daughter of a paratrooper-turned-teacher born in Torquay, Devon, Ms Mordaunt is a Royal Navy reservist, an acting sub-lieutenant of the Portsmouth-based HMS King Alfred and a former Minister of State for the Armed Forces.
She was elected MP for Portsmouth North in 2010, when she overturned Labour’s majority and has since increased her share of the vote in each of the following polls.
Before entering Parliament, she worked as head of broadcasting at the Conservative Party and advised politicians in the UK and overseas.
She worked as head of foreign press for George W Bush's presidential campaigns in 2000 and 2004.
Since her election in 2010, Mordaunt has consistently voted in favour of British military involvement overseas, according to the TheyWorkForYou website.
She voted to keep troops in Afghanistan in 2010 and in favour of airstrikes against Isis in Iraq in 2014 and in Syria in 2015.
She also voted against further investigations into the Iraq War in 2016 and supported the renewal of the Trident nuclear deterrent system in 2016.
Before the Brexit referendum, Ms Mordaunt campaigned to leave the EU.
She was criticised for endorsing a controversial Vote Leave poster that stoked fear over the possibility of Turkey joining the bloc. She also falsely claimed the UK would not have a veto over the membership of states such as Turkey – while Article 49 of the EU constitution requires a unanimous vote of all member states to allow access to a new member.
She had often voted against guaranteeing permanent rights to EU citizens after Brexit and refused to back Theresa May’s deal in December, prompting rumours she would quit Cabinet. Since then, she has almost always voted in line with other Conservative MPs.
In April 2018, Ms Mordaunt became minister for women and equalities, taking over from Amber Rudd after the Windrush scandal.
She has criticised the abortion ban in Northern Ireland and of Donald Trump’s global abortion restrictions, which bars women’s health charities involved in family planning from receiving US aid.
Outside of politics, Ms Mordaunt participated in ITV’s celebrity diving contest Splash! in 2014 andd worked as a magician’s assistant before entering university.
In 2014, she delivered a speech on poultry welfare for the sole purpose of saying “c**k” – which she said six times, adding “lay” or “laid” five times.
She later revealed she was fulfilling a forfeit presented to her during reservist training.
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