From: Fakhi Karume
In international diplomacy the terms “Ambassador” and “High Commissioner” are both used to refer to diplomats of the highest rank representing either a sovereign state or international organisation who is accredited to another sovereign state and or international organisation.
Since the 1815 Congress of Vienna, the status of Ambassadors has been defined and protected under international law as the recognized representatives of their respective heads of state who generally are also invested with “plenipotentiary powers”, meaning the full authority to represent their governments.
Their status as sovereign representatives explains why they are formally addressed as “His” or “Her Excellency” when at their external postings, as well as the need for them to present their credentials to the heads of state in the countries they are accredited to.
The term High Commissioner is reserved for those diplomats of Ambassador rank who are the head of a diplomatic mission of one Commonwealth government, such as Pakistan and Uganda, to another, such as Botswana. The use of the term “High Commission” as opposed to “Embassy” is in this context the proper designation for any Commonwealth nation’s diplomatic mission to another member state of the Commonwealth.