The 23-year-old was shot in the head by a Taliban gunman in Pakistan in 2012 after campaigning for girls to be educated in the country.
Malala, who graduated from the University of Oxford this summer, tweeted: “Covid-19 could force 20 million more girls out of school.
“To keep girls learning, we need leaders to prioritise education. Boris Johnson and Rishi Sunak: the UK pledged 0.7 per cent in aid last year.
“When you announce spending priorities...I hope you’ll deliver on that promise.”
She joins five former British Prime Ministers - Theresa May, David Cameron, Gordon Brown, Tony Blair and Sir John Major - who have reportedly called on Boris Johnson to rethink a proposed plan to cut the target from 0.7 per cent to 0.5 per cent.
Sir John told The Times any cuts to aid was “morally wrong and politically unwise”.
Kailash Satyarthi, who shared the 2014 Nobel Peace Prize for his work on children’s rights, has written to the Prime Minister, describing any reduction in aid as “immoral and dangerous”.
The 0.7 per cent target is written into law and Mr Johnson’s 2019 election manifesto promised to keep it.
The Tory 2019 manifesto said: “We will proudly maintain our commitment to spend 0.7 per cent of GNI on development, and do more to help countries receiving aid become self-sufficient.”
The Prime Minister’s official spokesman said: “The UK is and will remain one of the biggest contributors of aid of any country,” the spokesman said.
“But, as we have said, it is important to look at where savings can be made and to ensure that aid spending is used effectively.”
Mr Sunak will set out the budgets for Whitehall departments today against the tough economic backdrop of the coronavirus crisis.
Despite the mounting costs of coronavirus, the Treasury has already indicated that big sums will be spent on the NHS and other government priorities.
However, he was expected to start tightening the purse strings with a public sector pay freeze.