The Commonwealth realm of Guyana, officially known as "Guyana", was a predecessor to the modern-day Guyana and an independent state that existed between 26 May 1966 and 23 February 1970.
British rule ended in 1966, when Guyana was given independence as a Commonwealth realm by the Guyana Independence Act 1966 which transformed the British Crown Colony of British Guiana into the independent sovereign constitutional monarchy of Guyana with the British monarch as head of state. Guyana shared the Sovereign with the other Commonwealth realms, and the monarch's constitutional roles were mostly delegated to the Governor-General of Guyana. The royal succession was governed by the English Act of Settlement of 1701. The following governors-generals held office in Guyana during the dominion period:
- Sir Richard Luyt (26 May 1966 – 16 December 1966)
- Sir David Rose (16 December 1966 – 10 November 1969)
- Sir Edward Luckhoo (10 November 1969 – 1 July 1970)
Elizabeth II did not reside in or visit Guyana during its time as a Commonwealth realm.
The Republic of Guyana came into existence on 23 February 1970, when Guyana became a republic within the Commonwealth.
Forbes Burnham held office as prime minister (and head of government) of Guyana during this period. Following the abolition of the monarchy, former Governor-General Sir Edward Luckhoo provisionally became the first President of Guyana.