The monarchy of Antigua and Barbuda is a system of government in which a hereditary monarch is the sovereign and head of state of Antigua and Barbuda. The current Antiguan and Barbudan monarch and head of state, since 8 September 2022, is King Charles III. As sovereign, he is the personal embodiment of the Crown of Antigua and Barbuda. Although the person of the sovereign is equally shared with 14 other independent countries within the Commonwealth of Nations, each country's monarchy is separate and legally distinct. As a result, the current monarch is officially titled King of Antigua and Barbuda and, in this capacity, he and other members of the Royal Family undertake public and private functions domestically and abroad as representatives of Antigua and Barbuda. However, the King is the only member of the Royal Family with any constitutional role.

All executive authority is vested in the monarch, and royal assent is required for the Parliament of Antigua and Barbuda to enact laws and for letters patent and Orders in Council to have legal effect. Most of the powers are exercised by the elected members of parliament, the ministers of the Crown generally drawn from amongst them, and the judges and justices of the peace. Other powers vested in the monarch, such as dismissal of a prime minister, are significant but are treated only as reserve powers and as an important security part of the role of the monarchy.

The Crown today primarily functions as a guarantor of continuous and stable governance and a nonpartisan safeguard against the abuse of power. While some powers are exercisable only by the sovereign, most of the monarch's operational and ceremonial duties are exercised by his representative, the governor-general of Antigua and Barbuda.

The island of Antigua was explored by Christopher Columbus in 1493, and became a colony of Britain in 1632; Barbuda island was first colonised in 1678.

In 1736, Prince Klaas, an Afro-Antiguan slave, was elevated to the position of King of the Black Antiguans during an Akan ritual in Saint John's. This event was considered an "innocent ceremony" by white slave owners of Antigua, but was in fact a declaration of war. Prince Klaas planned a rebellion to establish Antigua as an independent state ruled by Africans. He planned to blow up a gunpowder barrel at a ball in honor of King George II, killing all Europeans and signaling allied slave Africans to attack any white person they saw, which would set off a chain of events that would result in Prince Klaas becoming the new King of Antigua. However, the plan was unsuccessful due to the identity of an unknown slave. Despite this, Prince Klaas remains a national hero in Antigua and Barbuda.

Having been part of the Federal Colony of the Leeward Islands from 1871, Antigua and Barbuda joined the West Indies Federation in 1958. With the breakup of the federation, it became one of the West Indies Associated States in 1967. Following self-governance in its internal affairs, independence was granted from the United Kingdom on 1 November 1981. Antigua and Barbuda became a sovereign state and an independent constitutional monarchy within the Commonwealth.

Princess Margaret represented her sister, Queen Elizabeth II, at the independence celebrations in the capital St John's. "Greetings from the Queen, welcome to the Commonwealth", Princess Margaret said at midnight after the flag-raising ceremony. A crowd of thousands cheered "Hip, Hip, Hooray" for the Queen and the prime minister. Wilfred Jacobs was sworn in as the first governor-general, the vice-regal representative of the Queen of Antigua and Barbuda. The Princess presented Antigua and Barbuda's instruments of independence to Prime Minister Vere Bird, formally declaring the country independent. The Princess opened the new Antigua and Barbuda Parliament building, and delivered the Speech from the Throne, on behalf of the Queen.

Antigua and Barbuda is one of fifteen independent nations, known as Commonwealth realms, which shares its sovereign with other monarchies in the Commonwealth of Nations, with the monarch's relationship with Antigua and Barbuda completely independent from his position as monarch of any other realm. Despite sharing the same person as their respective monarch, each of the Commonwealth realms — including Antigua and Barbuda — is sovereign and independent of the others. The Antiguan and Barbudan monarch is represented by a viceroy—the governor-general of Antigua and Barbuda—in the country.