[4] After graduating, Cregan was appointed judge's associate to John Doyle AC QC (Chief Justice of South Australia) and later served as an Australian Youth Ambassador for Development in Jakarta.

Cregan also held a number of board appointments with the Australian Property Institute and as a director of a family company.

Following the election of Steven Marshall's government in March 2018, Cregan was made Chair of the South Australian Public Works Committee with oversight of major infrastructure projects.

[6] On 12 October 2021, South Australia's Constitution Act was amended to adopt the United Kingdom practice of requiring an independent Speaker.

Following passage of the constitutional changes, Cregan was elected Speaker of the South Australian House of Assembly.