The King will host his first state visit as monarch later as he welcomes the South African president to the UK.
King Charles and Camilla, the Queen Consort, will host a banquet for President Cyril Ramaphosa at Buckingham Palace as part of the two-day trip.
Mr Ramaphosa is also set to address politicians in a joint sitting of both Houses of Parliament.
It is the first state visit to the UK in more than three years after they were stopped during the Covid pandemic.
The Prince and Princess of Wales will first greet the South African president at his London hotel on Tuesday morning and escort him to Horse Guards Parade for the ceremonial welcome with the King.
His Majesty will then ride down the Mall with Mr Ramaphosa in a carriage procession to Buckingham Palace.
There the King will host the president at a private lunch and show him an exhibition of Royal Collection items relating to South Africa.
Mr Ramaphosa, who has been head of government in South Africa since 2018, will follow the tradition of laying a wreath at the Tomb of the Unknown Warrior in Westminster Abbey, and then address MPs and peers in the Royal Gallery of the Palace of Westminster.
- Zim headed for a political dead heat in 2023
- Power crisis needs practical solutions
- Record breaker Mpofu revisits difficult upbringing
- Dangers of Arab Spring in SA
Later, the King will host a glittering white-tie banquet at Buckingham Palace for Mr Ramaphosa where both men will give speeches.
The visit follows the traditional format put in place during the reign of the late Queen Elizabeth II.
BBC southern Africa correspondent Pumza Fihlani says the president is hoping to use the state visit to drum up support for UK investment in South Africa to bolster the country's economic development and industries.
But his visit comes at a time when the head of state is facing criticism over South African unemployment levels and a return to power outages affecting households, businesses and schools across the country - almost every day for a number of hours at a time.
This month he also said he would "step aside" if charged over an alleged cover-up of a robbery at his private farm, which he denies.
This is the diplomatic equivalent of getting out the poshest plates and cutlery to impress the visitors.
Flags are out on the Mall, there will be a ceremonial carriage ride, honour guards and a banquet in Buckingham Palace.
The dinner service for the banquet dates back to George IV - and the motives, buttering up visiting dignitaries, are even older.
There is a serious soft-power intent behind the toasts and tiaras of the visit. Trade with South Africa represents 30% of the UK's entire trade with the African continent, worth almost £11bn per year.
The King is also now head of the Commonwealth and will want to send a positive message about strengthening relations.
There will also be sensitivity to concerns closer to home, with the backdrop of a deepening cost of living crisis. It will be red carpets, but with a purpose.
On Wednesday, the Earl of Wessex will escort Mr Ramaphosa to the Royal Botanic Gardens, at Kew in south-west London.
The South African leader will then visit Downing Street to meet Prime Minister Rishi Sunak, before returning to the palace to bid farewell to the King.
Mr Sunak said: "South Africa is already the UK's biggest trading partner on the continent, and we have ambitious plans to turbocharge infrastructure investment and economic growth together.
"I look forward to welcoming President Ramaphosa to London this week to discuss how we can deepen the partnership between our two great nations and capitalise on shared opportunities, from trade and tourism and security and defence."
The president is also set to receive a call from Labour leader Sir Keir Starmer and attend a Guildhall banquet with the Duke and Duchess of Gloucester.