Chris Wallace, whose stewardship of two presidential debates and penetrating interviews of world leaders made him the leading anchor of Fox News’s reportorial ranks, announced on Sunday that he had decided to leave the Rupert Murdoch-owned network after 18 years.

He will become an anchor for CNN+, the new streaming service from CNN that is expected to debut next year.

His exit from Fox News came as a surprise to the television news industry and will deprive the network of a prominent figure who has been the face of its influential Sunday program, “Fox News Sunday,” and the first anchor at the network to receive an Emmy Award nomination for his work.

“It is the last time, and I say this with real sadness, we will meet like this,” Mr. Wallace told viewers at the end of his Sunday broadcast.

“I want to try something new, to go beyond politics to all the things I’m interested in; I’m ready for a new adventure,” Mr. Wallace said. “And I hope you’ll check it out. And so for the last time, dear friends, that’s it for today. Have a great week. And I hope you’ll keep watching Fox News Sunday.”

Mr. Wallace covered the Reagan White House as an NBC News correspondent (and briefly moderated “Meet the Press”) before Roger Ailes, the co-founder of Fox News, hired him away from ABC News in 2003 to anchor the Murdoch network’s leading political news program.

An equal-opportunity interrogator of Democrats and Republicans, Mr. Wallace proved himself an outlier at times at Fox News, particularly in recent years when the network’s conservative opinion hosts closed ranks behind former President Donald J. Trump. Mr. Wallace’s criticisms of Mr. Trump earned rebukes from some viewers and the president’s own Twitter account, but he also irritated liberals who wished he would denounce his partisan colleagues.

In his on-air remarks on Sunday, Mr. Wallace said that “the bosses here at Fox promised me they would never interfere with a guest I booked or a question I asked, and they kept that promise. I have been free to report to the best of my ability, to cover the stories I think are important, to hold our country’s leaders to account. It’s been a great ride.”

The anchor’s contract was up at the end of this year, and the network had wanted to keep him on, according to a person familiar with internal deliberations. “Fox News Sunday” will temporarily be hosted by a rotation of the network’s news anchors, including Bret Baier, Martha MacCallum, John Roberts, Neil Cavuto, and others.

CNN said Mr. Wallace’s new program would appear on weekdays and “feature interviews with newsmakers across politics, business, sports and culture.”

In a statement distributed by CNN, Mr. Wallace said: “I look forward to the new freedom and flexibility streaming affords in interviewing major figures across the news landscape — and finding new ways to tell stories.”

As to Mr. Wallace’s departure, Fox News said in a statement: “We are extremely proud of our journalism and the stellar team that Chris Wallace was a part of for 18 years. The legacy of ‘Fox News Sunday’ will continue with our star journalists, many of whom will rotate in the position until a permanent host is named.”