Disclaimer: Answer from Google AI Overviews

The main difference is their relationship to the Commonwealth: an embassy is a diplomatic mission to a non-Commonwealth country, headed by an Ambassador, while a high commission is a diplomatic mission to a Commonwealth country, headed by a High Commissioner. Functionally, they perform the same role of representing their home government in the host country, but the term high commission is a legacy from the past when Commonwealth countries were not considered “foreign” to each other.

Embassy

  • Purpose: A diplomatic mission from a country to a non-Commonwealth country.
  • Head: The head of the mission is called an Ambassador.
  • Context: Represents a sending country in a non-Commonwealth country.
  • Activities: Engages in trade, cultural exchange, defense, and immigration, among other diplomatic functions, and maintains diplomatic relations with the host country.

High Commission

  • Purpose: A diplomatic mission from a Commonwealth country to another Commonwealth country.
  • Head: The head of the mission is called a High Commissioner.
  • Context: Represents a Commonwealth country in another Commonwealth country.
  • Activities: Nurtures foreign relations within the Commonwealth, strengthens bonds between member states, and engages in collaborative efforts to address global challenges, according to worldpassports.org.

In Summary

Embassy is the standard term for a diplomatic mission to a country that is not a member of the Commonwealth. High Commission is the equivalent term used between Commonwealth countries, a tradition stemming from the time when Commonwealth members did not view each other as fully foreign.