From 1966 to 1970 the head of state under the Constitution of 1966 was the queen of Guyana, Elizabeth II, who was also the monarch of the other Commonwealth realms.
Guyana became a republic within the Commonwealth under the Constitution of 1970 and the monarch and governor-general were replaced by a ceremonial president, by that time.
The governor-general was appointed for an indefinite term, serving at the pleasure of the monarch.
Since Guyana was granted independence by the Guyana Independence Act 1966, rather than being first established as a semi-autonomous dominion and later promoted to independence as defined by the Statute of Westminster 1931, the governor-general was to be always appointed solely on the advice of the Cabinet of Guyana without the involvement of the British government, with the sole exception of Richard Luyt, the former colonial governor, who served as governor-general temporarily until he was replaced by David Rose.
Currently, the president is both head of state and head of government and, pursuant to article 91 of the Constitution, is directly elected on the basis of the votes cast in the general election.