She was appointed parliamentary under secretary of state at the Department for Communities and Local Government in July 2014. Before this, she was parliamentary private secretary (PPS) to the secretary of state for defence, Philip Hammond from autumn 2013. 
In May 2015 Mordaunt became the first female armed forces minister at the Ministry of Defence. and was appointed minister of state for the Department for Work and Pensions by the incoming prime minister Theresa May on 15 July 2016.
Mordaunt worked for the Conservative Central Office where she was head of broadcasting under the leadership of William Hague. In 2000 she served as head of foreign press for George W. Bush’s presidential election campaign. 
- In Parliament, Mordaunt served on the European Scrutiny Committee, Defence Select Committee, and as chairman of the APPGs for Life Science and for Ageing and Older People.
- Mordaunt also worked as an aid worker in post-revolutionary Romania before and during university. She was director of communications at Kensington & Chelsea Council and the Freight Transport Association as well as being the a director at Diabetes UK. In 2004 she founded a media company, which she sold in 2010. 
- Media Intelligence Partners - former director
- Former associate at Hanover, a lobbying firm (2009)
- Terence Mordaunt - Conservative Party donor, is a relative
- Alex Black, Profile: Penny Mordaunt, Diabetes UK, PR Week, 4 May 2006.
- Penny Mordaunt, www.parliament.uk, accessed 4 September 2013.
- General Election: Penny Mordaunt holds Portsmouth North for Tories. The Portsmouth News, 7 May 2015, accessed 13 May 2015
- Ministerial appointments: July 2014, Prime Minister's Office, 15 July 2014.
- Penny Mordaunt GOV.UK, accessed 10 October 2014
- Penny Mordaunt first female Armed Forces Minister ITV News, 11 May 2015, accessed 13 May 2015
- Peter Geoghegan, Revealed: Climate change denier makes big donations to Boris Johnson and Jeremy Hunt, OpenDemocracy, 12 June 2019