Wolf joined just over a year ago and her contract expired in recent weeks.
While not contractually tied to The Guardian US, Wolf may still contribute in the future, the source said.
Wolf did not immediately respond for comment.
In addition to The Guardian, Wolf has contributed to The Washington Post, Harper's Baazar, and The Huffington Post and is the author of several books, including "The Beauty Myth."
UPDATE 8:58 pm: Politico's Dylan Byers reports that Wolf is in "early stage talks" with Al Jazeera. Although Wolf will no longer write weekly for the Guardian, she'll contribute monthly, scaling back writing duties while finishing her thesis at Oxford.
"Naomi will be a contributor to the Guardian, and write as her other commitments allow," a Guardian spokesperson said in an email.
The headline was changed to reflect that Wolf will still be contributing to the Guardian, albeit on a monthly basis.