An ambassador-at-large is a diplomat of the highest rank or a minister who is accredited to represent his country internationally.

Unlike an ambassador-in-residence who is usually limited to a country or embassy, the ambassador-at-large is entrusted to operate in several usually neighboring countries, a region or sometimes hold a seat in an international organization like the United Nations and the European Union. In some cases an ambassador-at-large may even be specifically assigned a role to advise and assist the state or a government in particular issues. Historically, presidents or prime ministers have designated special diplomatic envoys for specific assignments, primarily overseas but sometimes also within the country as an ambassador-at-large.