Images of updated banknotes featuring a portrait of the King will be revealed by the Bank of England by the end of this year.
Coins and banknotes featuring King Charles III and Queen Elizabeth II will co-circulate, under the plans.
Currency featuring the Queen will be replaced over time as coins and notes become damaged or worn.
The Royal Mint - which is has it's headquarters in Llantrisant - said that coins bearing the effigy of the King will enter circulation in line with demand from banks and post offices, and will circulate alongside coins featuring the Queen "for many years to come".
New banknotes featuring Charles are expected to enter circulation by mid-2024 and his portrait will appear on existing designs of all four denominations of banknote (£5, £10, £20 and £50).
This will be a continuation of the current polymer series and no additional changes to the banknote designs will be made, the Bank of England said.
In line with guidance from the Royal Household to minimise the environmental and financial impact of the change of monarch, existing stocks of notes featuring the Queen will continue to be issued into circulation, the Bank of England said.
New notes will only be printed to replace worn banknotes and to meet any overall increase in demand for banknotes.
Current banknotes featuring the portrait of the Queen will continue to be legal tender and will only be removed from circulation once they become worn or damaged, meaning they will co-circulate with those featuring Charles.
The Royal Mint said it will unveil further details about coins featuring the King over the coming weeks.
All UK coins bearing the effigy of the Queen will remain legal tender and in active circulation, the Mint said.
There are around 27 billion coins currently circulating in the UK bearing the effigy of the Queen. These will be replaced over time as they become damaged or worn, and to meet demand for additional coins.
Historically it has been commonplace for coins featuring the effigies of different monarchs to co-circulate. This ensures a smooth transition, with minimal environmental impact and cost.
Anne Jessopp, chief executive officer, the Royal Mint, said: "We are honoured to have struck each UK coin of her late majesty's reign, documenting her journey from young Queen to respected head of state.
"As official coin maker to the UK, we have told the story of each monarch since Alfred the Great and are now preparing for the biggest change in British coinage for several decades.
"The first coins bearing the effigy of His Majesty King Charles III will enter circulation in line with demand from banks and post offices. This means the coinage of King Charles III and Queen Elizabeth II will co-circulate in the UK for many years to come."