Muir will become the Anchor and Managing Editor of World News starting September 2.
"After wonderful years at World News I decided it is time to move to a new full time role at ABC News. I'll be joined by an incredible team of journalists dedicated to enterprise reporting, innovative approaches to breaking news and new ways of thinking about big issues and events around the world," Sawyer said. "I can't wait to continue bringing more of my specials to prime time and appearing on all ABC News broadcasts, as well. And to my friends and colleagues George and David -- congratulations. I look forward to exciting work together and great times ahead."
ABC also announced that Good Morning America anchor George Stephanopoulos, 53, is also stepping into a new role -- Chief Anchor of ABC News. In this position, Stephanopoulos will be the lead anchor for major special events and breaking news at ABC, and drive live network coverage.