Gillan began reporting for The Guardian in 1998 after seven years with other news organizations. After working in Iraq during the 2003 invasion, she was named Foreign Correspondent of the Year by the What the Papers Say Awards.
Pre-war reporting on bioterror and Iraq
On 15 October 2001, a letter addressed to United States Senator Tom Daschle was opened and found to contain anthrax spores. An article by Gillan dated 16 October stated that, "Iraq is known to have amassed enough weapons of mass destruction to enable them to wipe out the world's population." No source was provided for this statement, but Gillan made passing reference to New York Times journalist Judith Miller, who had published extensively on biological weapons. On 17 October 2001 Miller and Stephen Engelberg published a high-profile article in The New York Times that used an unidentified source to suggest a possible link between the anthrax attacks and Iraq. That Iraq had large stockpiles of biological weapons had been widely known since attempts in 1998 to convince the Clinton Administration to go to attack Iraq. 
Possible sources of anthrax terror
In addition to attempts to link the anthrax attacks to Iraq, efforts were being made by some to implicate both al-Qaida and another alleged Axis of evil member, North Korea. Gillan wrote, "Intelligence sources believe that Bin Laden operatives have been preparing for spectacular terrorist strikes using biological weapons for a number of years. It is believed that viruses causing deadly diseases such as ebola and salmonella were procured in Russia and that anthrax was obtained from North Korea." Again, the sources were not named. Letters included in the anthrax-containing envelopes attempted to link the anthrax to international terrorism, but the strain of anthrax used in the 2001 anthrax attacks was khown to be one used within the United States biological warfare program, not one known to be available to countries such as Iraq.
2003 Invasion of Iraq
Gillan was embedded with the Household Cavalry in Iraq during the invasion phase of Operation Telic. The Guardian has described Gillan as having been "given unique access to the Territorial Army in southern Iraq". Gillan described her role in Iraq as that of, "an independent witness, not working for the government."
- ^ Worldwide spread of anthrax panic: Biological weapons link to al-Qaida; FBI seeks evidence to connect hijackers, Iraq and germ warfare fears by Audrey Gillan. October 16, 2001 in The Guardian.
- ^ How Iraq's Biological Weapons Program Came to Light by William J. Broad and Judith Miller. February 26, 1998 in The New York Times.
- ^ Arsenal Could Kill Tens Of Millions by Martin Sieff. May 1, 1998 in The Washington Times Sieff wrote, "Iraq has enough deadly biological agents to kill every human being on earth."
- ^ The weekend warriors go to war by Audrey Gillan. October 14, 2004 in The Guardian.
- ^ Journalists offered Iraq war medals by Richard Norton-Taylor. February 24, 2004 in The Guardian.