Tom Llamas will take over as the anchor of NBC’s flagship news program, “NBC Nightly News,” the company said on Wednesday.

Mr. Llamas, 45, has been the anchor on the company’s streaming news outlet, NBC News Now. He succeeds Lester Holt, the longtime anchor of “NBC Nightly News,” who last month announced his plans to step down from the role.

The network said Mr. Llamas would take over “NBC Nightly News” this summer, assuming a lead anchor job that has been held by only three men — Tom Brokaw, Brian Williams and Mr. Holt — over the past 42 years.

Of course, the evening newscast does not have the same agenda-setting influence as it did during Mr. Brokaw’s tenure. But the newscasts still draw big audiences. Since September, “NBC Nightly News” has been attracting 6.3 million viewers a night, lagging ABC’s “World News Tonight” but remaining ahead of “CBS Evening News.”

In a statement, Mr. Llamas (pronounced YA-mas) said that taking over the anchoring duties was “a profound honor and one that carries tremendous responsibility.”

During the “Nightly News” afternoon editorial call on Wednesday, Mr. Holt called in from an Amtrak en route to New York from Washington and offered his congratulations. “It’s important to make the broadcast his, and you will over time, so we’ll make this transition work,” he said, according to a staff member who heard his remarks. “But I’m happy, happy for Tom and his family — crush it my friend.”

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