Fox News Channel anchor Megyn Kelly, a star of the US cable network's highly rated prime-time lineup, has decided to leave to join NBC News in a broad role that includes hosting a one-hour daytime news show.
Kelly also will anchor a Sunday night news show and take part in the network's special political programming and other big-event coverage, NBC News said in a statement on Tuesday.
The departure is a potential blow to Fox News, the top-rated cable news network, owned by Rupert Murdoch's 21st Century Fox .
Just months ago, its founding chairman, Roger Ailes, left following sexual harassment allegations by several women.
Kelly was one of the accusers and detailed Ailes' behaviour in her best-selling book, Settle for More. Ailes has denied the allegations.
Fox News, which is known for a roster of conservative commentators such as Bill O'Reilly, remained at the top of cable news ratings amid the Ailes turmoil. The network delivered its highest annual viewership in its 20-year history in 2016.
Kelly, 46, played a large role in that success, with 2.7 million viewers on average for her prime-time show, The Kelly File, second on Fox only to O'Reilly's program, The O'Reilly Factor.
"I have decided to end my time at FNC, incredibly enriched for the experiences I've had," Kelly wrote on Facebook.
She became a subject of news stories after Republican presidential candidate Donald Trump attacked her as unfair for her questioning of him at a primary debate during the 2016 election campaign.
Fox made a bid to keep Kelly, offering her more than $US20 million ($A28 million) a year, according to an October report in Vanity Fair.
In a statement on Tuesday, Murdoch thanked Kelly for "her 12 years of contributions" to the network.
"We hope she enjoys tremendous success in her career and wish her and her family all the best," Murdoch said.
Kelly will host her prime-time show on Fox News through to Friday.