Treadell joined the
Foreign and Commonwealth Office in 1978. From 2010 to 2014, she served as
High Commissioner to New Zealand and
Governor of Pitcairn. She is the first woman who served as British High Commissioner to
New Zealand. From October 2014 to 2019, she served as
High Commissioner to Malaysia. On 12 February 2019, Treadell was announced as the next
British High Commissioner to Australia, in succession to
Menna Rawlings, taking up the post in March 2019. In early February 2020, Treadell took the "unprecedented" step of giving two elected officials from the
Parliament of Australia a "dressing down". disapproval for how Australia had revealed its security concerns over the UK's invitation to Huawei into its 5G network, which had been expressed both to her, and her Foreign Secretary
Dominic Raab, in a private briefing. In 2021, she was branded as a "sanctimonious bore" by senior members of the Australian government over "publicly lecturing" Australia on its allegedly inadequate efforts to combat climate change. ==Personal life==