Archbishop Kay was born and studied in Melbourne. She was ordained Deaconess in 1984 and Deacon in 1986. In 1988 she was appointed Chaplain to Perth College and was among the first women in Australia to be ordained to the priesthood by Archbishop Peter Carnley in 1992.

Kay was appointed Assistant Bishop by Archbishop Roger Herft and was the first woman ordained to the episcopate in Australia on 22 May 2008.

In December 2014 Bishop Kay was elected to become the diocesan bishop of the Diocese of Gippsland and was installed on 21 March 2015.

In the Australian 2017 Queen's Birthday Honours List, she was appointed an Officer of the Order of Australia (AO) for "distinguished service to religion through the Anglican Church of Australia, as a pioneer and role model for women, to church administration, and to pastoral care and equality".

On 21 August 2017 Bishop Kay was elected as the Eight Archbishop of Perth and Metropolitan of the Province of Western Australia. On 10 February 2018 was installed as the first female archbishop in the Anglican Church of Australia.