The 62-year-old anchor broke the news on her Facebook.
Greta Van Susteren is leaving Fox News after 14 years with the network, and sources close to the situation tell ET that staffers were caught off guard by the announcement.
"Yes, I have left the Fox News Channel. On Thursday night, I made my decision and informed Fox News of my decision that I was leaving Fox News Channel per my contract," Susteren -- who has hosted On the Record since 2002 -- shared on Tuesday morning on Facebook. "Fox has not felt like home to me for a few years and I took advantage of the clause in my contract which allows me to leave now. The clause had a time limitation, meaning I could not wait."
Susteren said she hopes to continue her career in broadcasting, just not with the network. "I love my staff, I love my colleagues, and I love the crews. That is the hardest part of this decision as they are wonderful people," she wrote. "And most of all? I love the viewers -- even the ones who have gotten mad at me over the years and taken swipes."
"Everyone is shocked," one source tells ET of the 62-year-old anchor's exit. "We found out when the general public did. No email has gone out internally. Yet."
"[Susteren] had a 60-day window from the time Roger left to leave as well because she had a clause," a second source tells ET. "Bill O'Reilly and Sean Hannity also have clauses."
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Susteren's resignation comes on the same day that Gretchen Carlson settled her lawsuit with Fox News for a reported $20 million after she accused the network's former CEO and chariman, Roger Ailes, of sexual harassment in July. She alleged that he "sabotaged her career" because she "refused his sexual advances and complained about severe and pervasive sexual harassment."
Senior political analyst Brit Hume will take over as anchor of On the Record.
"21st Century Fox is pleased to announce that it has settled Gretchen Carlson's lawsuit," the media corporation said in a statement to ET on Tuesday. "During her tenure at Fox News, Gretchen exhibited the highest standards of journalism and professionalism. She developed a loyal audience and was a daily source of information for many Americans. We are proud that she was part of the Fox News team. We sincerely regret and apologize for the fact that Gretchen was not treated with the respect and dignity that she and all of our colleagues deserve."
In her own statement on Tuesday, Carlson said she was "ready to move on." The 50-year-old journalist, who was the anchor of The Real Story with Gretchen Carlson, had been with the network 11 years before exiting in July.
Reporting by Brendon Geoffrion