She was eventually transferred to Wellington, and when the Prime Minister's Department was founded in 1926, she took up a position with the nascent New Zealand diplomatic service.
[citation needed] Initially, McKenzie was secretary to Carl Berendsen, head of the Imperial Affairs Section.
The IAS was responsible for relations with the rest of the British Empire — other diplomatic activity was handled by Britain at the time.
She was part of New Zealand's delegation to an economic conference in Ottawa, and in 1936, she was posted to London, serving under High Commissioner Bill Jordan.
She then held positions in New Zealand's representation to Australia and the United Nations before finally being assigned to the new legation in Paris.