Explained: How Prince Harry and Meghan Markle can become King and Queen of the United Kingdom

The half-a-decade old royal battle has taken an emotional turn as Prince Harry, the younger son of King Charles III and Diana, expressed his deep desire to reconcile with his family, in a bombshell interview.
Noting that life is precious, and there's no point to fight anymore, the youngest son of King Charles, told BBC it would be nice to reconcile.
"I don't know how much longer my father has - he won't speak to me because of this security stuff but it would be nice to reconcile," he told the outlet.
Prince Harry, currently fifth in line to the British throne, recently lost a legal battle to reinstate taxpayer-funded security for himself and his family while in the UK.


Speaking from California, Harry said the dispute over security had become a major wedge in his relationship with his father, King Charles III. Despite the breakdown, Harry said he has “forgiven” his family and no longer wishes to fight, especially given uncertainty about how long his father, who was diagnosed with cancer last year, has left to live.
In February last year, Buckingham Palace announced that King Charles has cancer. However, it was not disclosed which form of cancer he suffered from. This has sparked discussions about ascension to the line of throne.

Prince William, as the eldest son of King Charles III, is first in line to the British throne. Upon the death of King Charles, William is expected to be crowned the next monarch, with his wife becoming Queen Consort—just as Camilla holds the title of Queen alongside King Charles. It is to be noted that she would not be styled as Queen Regnant, as she is not in the royal bloodline.
The crown passes to the descendants of Electress Sophia of Hanover, prioritizing direct heirs of the reigning monarch.
Given that Prince Harry and Meghan are not in direct line to the throne, and with no indication of changes to these laws, their ascension remains constitutionally unfeasible.
However, they may still ascend to the throne if the following 'very unlikely' events were to happen:

After Queen Elizabeth II died on September 8, 2022, after reigning for a record-breaking 70 years, her first-born Prince Charles ascended to the throne, becoming the British sovereign. Next in line of succession are King Charles's firstborn - Prince William, Prince of Wales, followed by William and Kate's firstborn, Prince George, currently 9-year old. Princess Charlotte, the second-born of William and Kate will be the next in succession - the third in line of the throne. Prince Louis, 4, comes fourth in the line of succession.

Prince Harry is fifth in line of succession, and can become King only if King Charles III, Prince William, and his children abdicate, or be otherwise removed from the line.
The British royal line of succession set by formal laws and constitutional conventions and not just tradition. Two of the most significant legal pillars are the Act of Settlement of 1701, which originally established that only Protestants could inherit the throne and excluded Catholics, and the Succession to the Crown Act of 2013, which modernized royal inheritance rules. The 2013 law ended male-preference primogeniture which allowed daughters to inherit the throne on equal footing with sons, and also permitted members of the royal family to marry Roman Catholics without losing their place in the line of succession.
The laws can be changed only through formal legislative action. That means a new law would need to be passed by the UK Parliament, approved by both Houses, and receive royal assent from the reigning monarch. However, since the monarch also serves as head of state in 15 other Commonwealth realms such as Canada, Australia, and New Zealand, any changes to the succession laws must be approved by the parliaments of all these nations under the Statute of Westminster (1931).
It appears highly unlikely that Prince Harry and Meghan Markle will ascend to the British throne anytime in the near future. Unless a series of extraordinary and historically unprecedented events, such as multiple abdications or sweeping legislative reform, were to occur, their path to becoming King and Queen remains, for now, firmly closed. However, with Harry and Meghan's current involvements in charitable and professional endeavours, it seems less likely that they wish to ascend to the throne after leaving the royal residence.