Major General Duncan Edward Lewis AO, DSC, CSC (born 3 August 1953) is an Australian military officer, diplomat and intelligence chief.

Prior to that appointment, he held the post of Australian Ambassador to the Kingdom of Belgium, the Grand Duchy of Luxembourg, the European Union and the North Atlantic Treaty Organization.

[4] Subsequent to his retirement from the army in 2005, Lewis joined the Australian Public Service and was appointed to the position of First Assistant Secretary of the National Security Division in the Department of the Prime Minister and Cabinet.

[6] On 17 September 2012, it was announced that Lewis had been appointed Australia's ambassador to Belgium, the European Union, Luxembourg and NATO, and would leave the Department of Defence on 10 October.

[9] On 15 May 2014, Foreign Minister Julie Bishop and Attorney-General George Brandis issued a joint media release announcing that Lewis was to stand down as Ambassador to Belgium, the EU, Luxembourg and NATO, and would be appointed as Director-General of Security (the head of the Australian Security Intelligence Organisation, Australia's domestic intelligence agency) following the retirement of David Irvine in September 2014.