Claire Coutinho has been appointed the new secretary for energy security and net zero, replacing Grant Shapps.
It is a significant promotion for the East Surrey MP who was only elected to Parliament in December 2019.
Rishi Sunak's decision to catapult her into the cabinet - as its youngest member - marks her out instantly as a major figure in Conservative politics, present and future.
She is the first member of the large 2019 intake of Tory MPs to make it to the cabinet table.
Before entering the Commons for the safe seat of East Surrey, Coutinho, 38, was an adviser to Mr Sunak, who at the time was chief secretary to the Treasury.
When Mr Sunak became chancellor in 2020 they effectively continued the partnership, with Ms Coutinho serving as his parliamentary aide.
She was a leading behind-the-scenes figure in Mr Sunak's leadership campaigns last summer, and is seen by colleagues as bright and competent, according to the BBC.
However, she faces a tough task in holding the differing wings of her party together over the government's commitment to net zero.
Labour's shadow climate change secretary Ed Miliband said her appointment "speaks volumes about the failures of Tory policy that we are now onto the sixth secretary of state since 2019".
"Reshuffling of the deckchairs will not deliver the proper energy policy Britain needs," he added.
Mr Shapps, who has held five ministerial jobs in the past year, has replaced Ben Wallace, who is leaving politics at the next election, as defence secretary.