[1] The Dominion of Canada and the colonies which preceded it had effectively engaged in diplomacy with Britain, particularly to promote their interests in immigration and economic matters, despite not being sovereign states.
In 1868, the Canadian Parliament sent Sir John Rose, 1st Baronet, as a "quasi-official representative" to Britain, and in 1878, with its growing political interests, Canada requested to send a full-time "resident minister to London" to engage in diplomacy with the British government.
The Colonial Office was amenable but felt that Canada's subordinate position in the British Empire precluded diplomatic status[a] and the diplomatic title "minister", and after some correspondence, Britain agreed to Canada's request for the title of "high commissioner", chosen to ensure that foreign governments understood its holder's importance.
Following the First World War, most of the dominions became founding members of the League of Nations and entitled to send diplomatic ambassadors to non-Commonwealth states.
[2] Canada exchanged high commissioners with other dominions during the Second World War, and afterwards with the newly-independent states of South Asia.