Theresa May is to make an "unashamed" vow to ensure overseas aid spending benefits UK interests while also seeking to give private firms greater confidence to invest in Africa.
The Prime Minister will use a speech to outline her ambitions for the continent after arriving as part of a three-day trade mission to South Africa, Nigeria and Kenya.
Mrs May is expected to declare her desire for the UK to overtake the United States to become the G7's leading investor in Africa by 2022, amid warnings of "greater conflict and an increased susceptibility to extremism" emerging if jobs are not created.
Downing Street believes helping young people in Africa secure jobs will stabilise the economy of their country while also reducing the likelihood of them undertaking risky journeys to Europe.
The PM is also expected to reassert the UK's shift in strategy over aid spending - using the trip to encourage private sector investment alongside efforts to alleviate extreme poverty.
Britain's overseas aid budget totalled £13.9 billion in 2017, an increase of £555 million in 2016 and in line with the legal commitment to invest 0.7% of national income in this area.
It has proven a controversial pledge among some Tory backbenchers, with successive international development secretaries vowing to use the cash to help develop trade against the backdrop of Brexit.
Mrs May is expected to use her speech to outline investment in Britain's diplomatic network in Africa, with the use of trade experts to help encourage investment, amid growing influence on the continent from other countries including China.
Business leaders and ministers, including the international trade department's George Hollingbery, are accompanying Mrs May on her first visit to Africa as PM which includes meetings with the presidents of each country on her agenda.
Speaking at the First National Bank in Cape Town on Tuesday, Mrs May is expected to say the private sector is key to driving growth in labour markets and "unleashing the entrepreneurial spirit" in Africa.
She will say: "However, for a variety of reasons the private sector has not yet managed to deliver the level of job creation and investment that many African nations need.
"So I want to put our development budget and expertise at the centre of our partnership as part of an ambitious new approach - and use this to support the private sector to take root and grow."
Mrs May will add: "I am unashamed about the need to ensure that our aid programme works for the UK.
"So today I am committing that our development spending will not only combat extreme poverty, but at the same time tackle global challenges and support our own national interest. This will ensure that our investment in aid benefits us all, and is fully aligned with our wider national security priorities."
Downing Street cited data from the United Nations Conference on Trade and Development (UNCTAD) as showing UK direct investment in Africa was 55 billion US dollars (£42.7 billion) in 2016 compared to 57 billion US dollars (£44.3 billion) from the US.
France followed in third with 49 billion US dollars (£38 billion) and China fourth with 40 billion US dollars (£31 billion).
Mrs May will outline her ambition for the UK to be the G7's "number one investor in Africa" by 2022, adding Britain's private sector should invest the billions that will see "African economies growing by trillions".
The PM will add: "It is in the world's interest to see that those jobs are created, to tackle the causes and symptoms of extremism and instability, to deal with migration flows and to encourage clean growth.
"If we fail to do so, the economic and environmental impacts will swiftly reach every corner of our networked, connected world.
"And the human impacts - from a loss of faith in free markets and democracy as the best way to secure global growth and human rights, to greater conflict and an increased susceptibility to extremism - will be similarly global."
Among Mrs May's business delegation are Charles Bowman, Lord Mayor of the City of London Corporation, David Schwimmer, CEO of the London Stock Exchange, and representatives of firms who specialise in helping Africa - including Georgia Barrie, co-founder and director of Farm.ink, which helps farmers connect and share information.
During her trip to South Africa, Mrs May will also hold a bilateral meeting with president Cyril Ramaphosa and hopes to visit Robben Island - where Nelson Mandela was imprisoned during the era of Apartheid.
Such a visit would commemorate the 100th anniversary of the former South African president's birth.