Donald John Markwell AM (born 19 April 1959) is an Australian social scientist, who has been described as a "renowned Australian educational reformer". He was appointed Head of St Mark's College, Adelaide, from November 2019. He was Senior Adviser to the Leader of the Government in the Australian Senate from October 2015 to December 2017, and was previously Senior Adviser on Higher Education to the Australian Minister for Education.

Markwell was born in Quilpie, Queensland. He was educated at Brisbane Grammar School followed by the University of Queensland, the University of Oxford (where he was the 1981 Rhodes Scholar for Queensland) and Princeton University. He studied economics, law and international relations.

Markwell was a research fellow of New College, Oxford, from 1985 to 1986, and then a fellow and tutor in Politics at Merton College, Oxford, from 1986 to 1997. He served as a reforming warden (CEO) of Trinity College (University of Melbourne) from 1997 to 2007; deputy vice-chancellor (Education) of the University of Western Australia from 2007 to 2009; and warden of Rhodes House, Oxford, from 2009 to 2012 (succeeding Sir Colin Lucas).

From 2007 to 2009, Markwell led a curriculum review at the University of Western Australia. The review proposed significant curriculum reform; it was implemented as "New Courses 2012".

Markwell was the first Rhodes Scholar and the second Australian to serve as warden of Rhodes House (the global CEO of the Rhodes Trust and the Rhodes Scholarships). As warden from 2009 to 2012, Markwell expanded activities for Rhodes Scholars in Oxford, expanded alumni communications, events and consultation, initiated governance reform and raised significant funds to support the Rhodes Scholarships. The appointments of several new Rhodes trustees from around the world included John MacBain, who was later recognized as the "Second Century Founder" of the Rhodes Trust for a gift of £75 million. As well as discussing leadership, liberal education and collegiate education, Markwell's speeches drew attention to Cecil Rhodes' goal of promoting international peace. He initiated discussion on increasing the number of countries in which Rhodes Scholarships are offered, leading to the later creation of Rhodes Scholarships for China and other countries. He is credited with helping to initiate the review of undergraduate women's leadership at Princeton University, chaired by Nannerl O. Keohane, and of helping to make scholarships in South Africa open to women.

In 2012, Markwell stepped down as warden of Rhodes House to return to Australia, where his family lives, and to become the executive director of the Menzies Research Centre. The chairman of the Rhodes Trust, John Hood, paid tribute to "the extraordinary energy and commitment Markwell has brought to the advancement of the Rhodes Trust's affairs", and to the "many notable accomplishments under his leadership".

As executive director of the Menzies Research Centre (a public policy think tank in Australia named for Australia's longest-serving prime minister, Sir Robert Menzies, and associated with the Liberal Party of Australia), his activities included consultations with Julie Bishop for developing a 'New Colombo Plan' to encourage Australian university students to study abroad in Asia-Pacific universities, and co-editing State of the Nation: aspects of Australian public policy.

In October 2013, following the Australian federal election of September 2013, Markwell was appointed as senior adviser on higher education to the new Australian minister for education, Christopher Pyne, MP. In October 2015, after the change of prime minister from Tony Abbott to Malcolm Turnbull, he became senior adviser to the new leader of the government in the Australian Senate, George Brandis, who was also Attorney-General of Australia, until December 2017. Markwell gave constitutional advice to the Prime Minister and Attorney-General during the prorogation, recall, and double dissolution of the Australian Parliament in 2016.