Weir's move is scheduled to take place in November, at which point he'll remain in New York and help CNN producers develop original programming, the Los Angeles Times reported Friday.
"Bill's range, sensibility and curiosity set him apart," CNN Worldwide President Jeff Zucker said in a statement. "He brings a unique storytelling style, perspective and sense of humor to CNN, and he will be a key player as we continue to expand our lineup."
"Good Morning America" co-anchor Dan Harris will take Weir's place on "Nightline," but will also continue his position on the morning show, the newspaper said.
'SNL': 'Anchorman 2' cast, One Direction sing 'Afternoon Delight' [VIDEO]
Reindeer recovered after escaping from Santa during lighting ceremony