It is being held at Westminster Abbey on 6 May and the King, who will be crowned along with Camilla, the Queen Consort, will be the 40th reigning monarch crowned there since 1066.
The day of splendour and formality will feature customs dating back more than 1,000 years. Here is how we expect it to unfold.
The formal celebrations will begin with a procession from Buckingham Palace to Westminster Abbey with viewing areas along the route opening at 06:00 BST.
Public access to sites along The Mall and Whitehall will be on a first-come, first-served basis, with people directed to official screening sites in Hyde Park, Green Park and St James's Park once they are full.
Stands for invited guests, including armed forces' veterans and NHS and social care staff, have been erected outside Buckingham Palace.
Just under 200 members of the armed forces - most from the Sovereign's Escort of the Household Cavalry - who will be taking part in the procession to Westminster Abbey will start to gather on Saturday morning.
Another 1,000 service personnel will line the route, but the overall procession will be much smaller than its equivalent in 1953 when other royal families and Commonwealth prime ministers were among those who took part.
The procession will set off from Buckingham Palace at 10:20 BST (05:20 EDT) moving along The Mall to Trafalgar Square, then down Whitehall and Parliament Street before turning into Parliament Square and Broad Sanctuary to reach the Great West Door of Westminster Abbey.
In a break from tradition, King Charles and Queen Consort Camilla will be in the Diamond Jubilee State Coach rather than the older, more uncomfortable, Gold State Coach.
The procession is expected to arrive at the abbey shortly before 11:00, with the King likely to wear military uniform instead of the more traditional breeches and silk stockings worn by kings before him.
King Charles will enter through the Great West Door and proceed through the nave until he reaches the central space in the abbey.
He will be preceded by processions made up of faith leaders and representatives, and representatives from some Commonwealth countries who will carry the flags of their country and be accompanied by the governors general and prime ministers. These will include UK Prime Minister Rishi Sunak, who will also give a reading later in the service.
The ceremony is due to begin at 11:00 and will be punctuated with music selected by the King, with 12 newly commissioned pieces, including one by Andrew Lloyd Webber, and Greek Orthodox music in memory of the King's father, Prince Philip.
The King's grandson, Prince George, will be among the pages at Westminster Abbey, alongside Camilla's grandchildren, Lola, Eliza, Gus, Louis and Freddy. Some of those taking part in the procession inside the abbey will carry the regalia ahead of the King, with most items placed on the altar until needed in the ceremony.
The UK is, according to the Royal Family website, the only European country that still uses regalia - the symbols of royalty like the crown, orb and sceptres - in coronations.
The individual objects symbolise different aspects of the service and responsibilities of the monarch.
Charles will be presented with the Sovereign's Orb, the Sovereign's Sceptre with Cross, and the Sovereign's Sceptre with Dove and other items at key moments in the ceremony.
And Camilla will be presented with the Queen Consort's Rod with Dove and the Queen Consort's Sceptre with Cross - mirroring the King's sceptres.
There are several stages to the service, which is expected to last a little under two hours.
For the first time members of the public will be invited to pledge their allegiance to the King, in a part of the service organisers are calling the "chorus of millions". In another departure from tradition, female clergy will play a prominent role and religious leaders from other faiths will have an active part.
King Charles will be presented to "the people" - a tradition dating back to Anglo-Saxon times. Standing beside the 700-year-old Coronation Chair, the King will turn to face the four sides of the abbey and be proclaimed the "undoubted King" before the congregation is asked to show their homage and service.
Archbishop of Canterbury Justin Welby will make the first declaration but, for the first time, the subsequent declarations will be made by the Lady of the Garter and the Lady of the Thistle - representing the oldest orders of chivalry in England and Scotland respectively - and a George Cross holder from the armed forces.
The congregation will shout "God Save the King!" and trumpets will sound after each recognition.
The Coronation Chair, also known as St Edward's Chair or King Edward's Chair, is believed to be the oldest piece of furniture in the UK still used for its original purpose. A total of 26 monarchs have been crowned in it.
It was originally made by order of England's King Edward I to enclose the Stone of Destiny, which had been taken from near Scone in Scotland.
The stone - an ancient symbol of Scotland's monarchy - was returned to Scotland in 1996 but has been transferred back to London for use in the service.
During the Coronation, the oak chair is placed in the centre of the historic medieval mosaic floor known as the "Cosmati pavement", in front of and facing the high altar, to emphasise the religious nature of the ceremony.
Just before the oath, the Archbishop of Canterbury will acknowledge the multiple faiths observed in the UK by saying the Church of England "will seek to foster an environment in which people of all faiths may live freely".
The archbishop will then administer the Coronation Oath - a legal requirement. He will ask King Charles to confirm that he will uphold the law and the Church of England during his reign, and the King will place his hand on the Holy Gospel and pledge to "perform and keep" those promises.
The King will also take a second oath - the Accession Declaration Oath - stating that he is a "faithful Protestant".
The King's ceremonial robe will be removed and he will sit in the Coronation Chair to be anointed, emphasising the spiritual status of the sovereign who is also the head of the Church of England.
The archbishop will pour special oil from the Ampulla - a gold flask - on to the Coronation Spoon before anointing the King in the form of a cross on his head, breast and hands.
The Ampulla was made for Charles II's coronation, but its shape harks back to an earlier version and a legend that the Virgin Mary appeared to St Thomas a Becket in the 12th Century and gave him a golden eagle from which future kings of England would be anointed.
The Coronation Spoon is much older, having survived Oliver Cromwell's destruction of the regalia after the English Civil War.
The oil itself was produced for the coronation using olives harvested from two groves on the Mount of Olives in Jerusalem, and consecrated at a special ceremony at the Church of the Holy Sepulchre in the city.
A screen will be arranged around the chair to conceal the King from view, because this is considered to be the most sacred part of the service.
Literally the crowning moment - when the King will wear St Edward's Crown for the only time in his life.
The crown is named after a much earlier version made for the Anglo-Saxon king and saint, Edward the Confessor, and said to have been used at coronations after 1220 until Cromwell had it melted down.
It was made for King Charles II, who wanted a crown similar to the one worn by Edward but even grander.
King Charles III will be only the seventh monarch to wear it after Charles II, James II, William III, George V, George VI and Elizabeth II - who last wore it at her own coronation in 1953.
First the King will be given a shimmering golden coat to wear called the Supertunica, and be presented with items including the Sovereign's Orb, the Coronation Ring, the Sovereign's Sceptre with Cross and the Sovereign's Sceptre with Dove.
Then the archbishop will place St Edward's Crown on the King's head and the abbey bells will ring for two minutes, trumpets will sound and gun salutes will be fired across the UK.
A 62-round salute will be fired at the Tower of London, with a six-gun salvo at Horse Guards Parade. Twenty-one rounds will be fired at a further 11 locations around the UK, including Edinburgh, Cardiff and Belfast, and on deployed Royal Navy ships.
The final part of the ceremony will see the King take the throne. He may even be lifted into it by the archbishop, bishops and other peers of the kingdom.
Traditionally, a succession of royals and peers would then have paid homage by kneeling before the new king, swearing allegiance and kissing his right hand.
However, Prince William will be the only Royal Duke to kneel and pay homage to King Charles.
And instead of peers, for the first time the archbishop will invite people in the abbey, and those watching and listening at home, to pledge allegiance in what is called a "new and significant moment in the tradition of the coronation" by organisers.
After the homage, Queen Camilla will be anointed, crowned and enthroned in a simpler ceremony - although she will not have to take an oath.
She will be crowned with Queen Mary's Crown - originally made for Queen Mary's coronation alongside George V - but it is being modified to remove some of the arches and reset with the Cullinan III, IV and V diamonds.
The final part of the service will see the King and Queen taking Holy Communion - the principal act of worship of the Christian church.
Full details of the service for the Coronation can be found on the Church of England website.
The King and Queen Consort will descend from their thrones and enter St Edward's Chapel behind the high altar - here Charles will remove St Edward's Crown and put on the Imperial State Crown before joining the procession out of the abbey as the national anthem is played.
The King and Queen Consort will then return to Buckingham Palace along the reverse of the route by which they came, this time travelling in the 260-year-old Gold State Coach that has been used in every coronation since William IV's.
Reports suggest the Prince of Wales' three children, princes George and Louis and Princess Charlotte, will join the procession with their parents, in a carriage behind the Gold State Coach.
Nearly 4,000 members of the UK's armed forces will be taking part in what the Ministry of Defence has called the largest military ceremonial operation of its kind for a generation.
They will be joined by representatives from Commonwealth countries and the British Overseas Territories.
And the Royal British Legion will provide a 100-strong guard of honour to line the procession route in Parliament Square.
The route is 1.42 miles (2.29km) from the abbey right into the palace grounds. The King and Queen will receive a Royal Salute and three cheers from military personnel who have been on parade.
In 1953, the route was more than four miles long and it took 45 minutes for the whole procession to pass a single point.
It has become customary since the coronation of Edward VII in 1902 for the new monarch to greet the crowds in The Mall from the Buckingham Palace balcony - the Queen was joined by her mother, children and sister among other royals as she watched a fly-past involving hundreds of planes in 1953.
Buckingham Palace has confirmed that King Charles and Queen Camilla will continue the tradition - although which other members of the Royal Family will be involved has not yet been confirmed.
Those there will witness the end of the day's public celebrations at 14:30, with a six-minute fly-past involving members of the Army, Royal Navy and Royal Air Force and culminating in a display by the Red Arrows.