Mordaunt, who has joined the charity as director of nations, regions and campaigns, has been given a brief to increase the organisation's political clout.
'I have a very political background and you will start to notice a change in the charity's direction in that respect,' said Mordaunt.
'Diabetes UK's work concerns both future and current public health issues, and we are working on some of the healthcare headaches facing the Government.'
The charity has been quick to seize on healthy eating and anti-obesity messages, recently producing figures showing overweight people to be 80 times more likely to develop type-2 diabetes than those at a healthy weight. It is also leading the fight to get the National Institute of Clinical Excellence to approve a new insulin inhaler after draft guidance published by NICE said the benefits did not outweigh the costs.
Mordaunt said one of the charity's biggest publicity challenges was to seek out the 'missing millions' of people with diabetes, who are currently undiagnosed, and help them manage the condition.
Mordaunt left Kensington and Chelsea three years ago, and founded political consultancy Media Intelligence Partners with ex-Tory central office media director Nick Wood.
Before that, she was deputy director of comms for the Big Lottery Fund and head of broadcasting for the Tory party under William Hague in 2001. She also stood as Conservative candidate for Portsmouth in the 2005 general election.
Mordaunt replaces Benet Middleton, who left in January, and will head up a team of 77. It is made up of eight regional and three national offices, public affairs and press teams and a volunteer development team. She reports to chief executive Douglas Smallwood.