One of Fox News’ most popular primetime hosts, Tucker Carlson, is leaving the network effective immediately, Fox News said in a terse statement Monday. His last show on the network was Friday, April 21.

“Fox News media and Tucker Carlson have agreed to part ways,” the statement said. “We thank him for his service to the network as a host and prior to that as a contributor.”

Beginning Monday night, the 8 p.m. slot previously filled by Mr. Carlson’s eponymous show, Tucker Carlson Tonight, will be filled by a show titled Fox News Tonight helmed by what was described as a rotating collection of Fox News personalities until a new host can be named.

No reason was given immediately for Mr. Carlson’s departure, but the abruptness of the announcement and the fact that he will not be airing a final show suggests that the separation was not something that had been planned.

The separation comes just days after Fox agreed to settle a defamation case against it by Dominion Voting Systems for more than $787 million. In its lawsuit, Dominion said Fox and its primetime personalities — including Mr. Carlson — defamed the company by repeating claims from President Trump and his lawyers that the company somehow rigged the 2020 election against him. Mr. Carlson was widely expected to testify had the case gone to trial.

Mr. Carlson’s show was consistently one of the highest-rated offerings on the network — indeed, in all of cable news — with more than 3 million nightly viewers. He was one of the network’s most vociferous supporters of Mr. Trump.