Greta Van Susteren, who has hosted a top-rated evening program at Fox News for 14 years, is leaving the network.

The abrupt announcement today, in the middle of the presidential campaign, was coupled with word that Brit Hume, Fox’s senior political analyst and a former Washington managing editor, will take over as host of “On the Record” through the election.

Van Susteren, an attorney who hosted a legal show at CNN before joining Fox, has had a richly varied career, from interviewing presidential candidates to flying off to disaster zones such as Haiti, where she opened an orphanage and school named after her. The Wisconsin native has also been a forceful presence online, with her blog and with more than 1 million Twitter followers.

Bill Shine and Jack Abernethy, recently named co-presidents of Fox News, said in a joint statement: “We are grateful for Greta’s many contributions over the years and wish her continued success.” They also praised Hume as “one of the best political analysts in the industry” and “the ideal choice to host a nightly political program while the most dynamic and captivating election in recent history unfolds.”

Hume said he is “happy to take on this assignment for the balance of this extraordinary election. My Fox News colleagues have set a high standard for political coverage which I’ll do my best to uphold. I’m honored to be asked.”

According to a source familiar with the process, Van Susteren asked to renegotiate her contract after Roger Ailes resigned under pressure as Fox News chairman following a sexual harassment lawsuit. Van Susteren is one of a number of key Fox personnel whose contract included a “key man” clause allowing her to leave if Ailes departed.

When those negotiations deadlocked, Van Susteren chose to invoke the departure option, the sources said. Her last show was Thursday, and the swiftness of events did not allow her to deliver an on-air farewell.

Hume, who spends part of the year in Florida, is not interested in taking over the Washington-based show permanently. The sudden vacancy could set off a competition to fill the 7 p.m. ET slot.

This would be among the first major programming decisions made by Rupert Murdoch since the network’s owner stepped in as acting CEO of Fox News after Ailes’ resignation.