Mr. Williams is expected to move to a new role at NBC News, primarily at the cable news network MSNBC, which would probably be in a breaking-news capacity at the beginning, according to one of the people.

Lester Holt, who has been filling in for Mr. Williams as anchor, will permanently assume the position as anchor of NBC’s evening newscast, one person said. Mr. Holt was previously the anchor of NBC’s weekend evening news broadcasts.