Dr De Jersey practiced law in Queensland and was called to the Queensland Bar in 1971. He took silk in 1981 as a Queen's Counsel.
At the bar, De Jersey practiced in the commercial field; appeared in constitutional cases before the High Court of Australia, and also appeared before the Judicial Committee of the Privy Council. He was appointed a judge of the Supreme Court of Queensland in 1985 and was the commercial causes judge between 1986 and 1989. He was the judge constituting the Mental Health Tribunal between 1994 and 1996, the president of the Queensland Industrial Court between 1996 and 1997, and the chairman of the Law Reform Commission of Queensland from 1996 to 1997.
De Jersey was appointed Chief Justice of Queensland on 17 February 1998. He has been the chancellor of the Anglican Diocese of Brisbane since 1991. He was also the vice president of the Australian Cancer Society between 1995 and 1998 and its president between 1998 and 2001, a trustee of the National Breast Cancer Foundation between 1994 and 1999, and the chairman of the Queensland Cancer Fund (now The Cancer Council Queensland) between 1994 and 2001.
De Jersey became the 26th Governor of Queensland on 29 July 2014. On the retirement of Alex Chernov as Governor of Victoria on 1 July 2015, de Jersey became the longest-serving sitting governor of an Australian state and by custom assumed the additional office of Administrator of the Commonwealth who exercises the powers of the Governor-General of Australia in the governor-general's absence or disability.