A High Commissioner is a person serving in a special executive capacity.
In the Commonwealth of Nations, a High Commissioner is the senior diplomatic envoy of one Commonwealth Government another. As many Commonwealth members share the same head of state (Queen Elizabeth II), Commonwealth diplomatic relations are technically at a governmental level, and Commonwealth Governments thus do not appoint ambassadors, who are the representatives of one head of state to another. For historical reasons, High Commissioners are appointed even in the case of Commonwealth republics that do not have the Queen as head of state. In the place of an embassy is a High Commission. Outside the capital city Commissioners are appointed instead of consuls, although the Commissioner's mission is generally known as a consulate as opposed to a commission.
Despite the differences in terminology, since 1948 Commonwealth High Commissioners have enjoyed the same diplomatic rank and precedence as ambassadors of foreign heads of state, and in some countries are accorded privileges not enjoyed by foreign ambassadors. For example, the Queen receives high commissioners before ambassadors, and sends a coach and four horses to fetch new high commissioners to the palace, whereas new ambassadors only get two horses. Commonwealth high commissioners also play a part in important ceremonies of state, such as the annual Remembrance Sunday service at the Cenotaph in Whitehall, and royal funerals.
Historically, in the British Empire High Commissioners were envoys of the Imperial Government appointed to manage protectorates or groups of territories not fully under the sovereignty of the British Crown. Such High Commissioners were also charged with managing diplomatic relations with native rulers and their states, and might have under them several Resident Commissioners attached to each state. In certain places of particular importance, a Commissioner-General would be appointed, who would have control over several High Commissioners and Governors, e.g. the Commissioner-General for South-East Asia had responsibility for Malaya, Singapore and British Borneo. The title of High Commissioner was also used for the administrators of mandates and trust territories, e.g.British Mandate of Palestine.
In contrast, crown colonies (which were British sovereign territory) would normally be administered by a Governor, while the most significant possessions, confederations and the independent Commonwealth Dominions would be headed by a Governor-General.
The first Dominion High Commissioner was appointed by Canada as its envoy in London in 1880, however the Imperial Government did not appoint high commissioners to the Dominions, where it was already represented by the relevant Governor-General. This began to prove problematic after the First World War when the dominions demanded a far greater degree of control over their foreign affairs. In Canada matters would come to a head during the King-Byng Affair of 1926.
The Imperial Conference of 1929 established that the Governors-General in the independent Dominions were not the representatives of the United Kingdom Government but the personal representatives of the Sovereign, and with the constitutional development of the Dominions and their assumption of control over their own external and foreign relations, it became standard for the United Kingdom and the Dominions to exchange high commissioners to each other's Governments.
From as early as the 1930s, some Commonwealth members have indicated a preference for the title to be replaced with that of ambassador, but over the years whenever the issue has been raised a majority of members has been in favour of keeping the separate title and status of high commissioner.
- History of the title High Commissioner (http://www.psa.ac.uk/publications/psd/1998/lloyd1.htm)
At the United Nations, a High Commissioner serves a commission composed of representatives of various nations. For instance, the U. N. High Commissioner for Human Rights serves the United Nations Human Rights Commission.