Briton Jacqueline Sutton, 50, was found hanged Saturday in a restroom at the airport's international transit terminal, Turkey's state-sponsored Anadolu news agency reported, citing Istanbul police.
Sutton, who once worked for the United Nations and the BBC, flew from London to Istanbul to take a connecting flight to her base in Irbil in the Kurdish region of northern Iraq, according to her employer, the Institute for War and Peace Reporting
Turkish media reported Sutton missed her flight to Irbil.
Britain's Foreign and Commonwealth Office confirmed the death of a British national in Turkey, saying embassy staff was assisting the family of the deceased and that British officials would remain in close contact with Turkish authorities.
Anadolu reported that Sutton hanged herself, citing Turkish security officials. Turkish authorities have not responded to CNN requests for comment.
'Don't believe the reports'
News of Sutton's death caused an outpouring of grief on Twitter, with friends and former colleagues expressing skepticism she could have taken her own life and calling for a full investigation into her death.
"Simply don't believe the news reports," tweeted Jane Pearce, Iraq country director for the U.N. World Food Program, describing Sutton as a friend.
Sudipto Mukerjee, a former colleague of Sutton's from the U.N. Development Program, tweeted that he found it "very difficult" to believe the reports of suicide.
Charlie Winter, a senior researcher at London-based counter-extremism organization Quilliam, wrote that he did not "for 1 second believe" that Sutton had taken her own life. "When we met on Monday she was engaging, driven; seemed anything but suicidal," he tweeted.
The Melbourne, Australia-based International Women's Development Agency tweeted it would "be seeking answers and calling for urgent action" over Sutton's death.
John MacLeod, managing editor of the London-based Institute for War and Peace Reporting, told CNN that Sutton's employer was sending staff to Turkey to seek answers from officials.
MacLeod said he did not know what to think of suggestions her death could be attributed to something other than suicide.
"We don't honestly know," he said. "Obviously the circumstances are unclear. ... We will be looking to ask for a thorough investigation."
Group's second Iraq country director to die
Sutton was appointed the organization's acting country director in Iraq in June, replacing Ammar Al Shahbander, who died in a May car bomb attack in Baghdad. She had been in London last week to attend a memorial service for Al Shahbander, the institute said.
The organization added in a statement that Sutton "was returning to Iraq full of plans for innovative new work, including projects to counter violent extremism that threatens a country to which she was so committed."
"Jacky was one of the top development professionals working on Iraq, and she devoted nearly 10 years of her life to helping the country," said Anthony Borden, the institute's executive director.
"She was extremely bright, highly competent, and well able to handle herself in difficult environments, and she was universally loved. We are in total shock."
Sutton spoke five languages, including Arabic, and had extensive experience in media and development fields, having worked for the BBC in Africa, the Middle East and the United Kingdom, and in senior roles for the United Nations from Afghanistan and Iran to Gaza and West Africa.
She had recently been pursuing a doctorate on the position of female journalists in Iraq and Afghanistan, studying at the Center for Arab and Islamic Studies at the Australian National University in Canberra, the Institute for War and Peace Reporting said.