The cause of his death apparently was an asthma attack, the Times said. Times photographer Tyler Hicks was with him and carried his body to Turkey, it said.
Shadid, a 43-year-old American of Lebanese descent, had a wife and two daughters. He had worked previously for The Associated Press, The Washington Post and The Boston Globe. He won the Pulitzer Prize for international reporting in 2004 and 2010 for his Iraq coverage.
Shadid had been reporting in Syria for a week, gathering information on the resistance to the Syrian government, the Times said. The exact circumstances and location of his death were unclear, it said.
Speaking to an audience in Oklahoma City about a month after his release, he said he had a conversation with his father the night before he was detained.
"Maybe a little bit arrogantly, perhaps with a little bit of conceit, I said, `It's OK, Dad. I know what I'm doing. I've been in this situation before,"' Shadid told the crowd of several dozen people. "I guess on some level I felt that if I wasn't there to tell the story, the story wouldn't be told."