David Muir to Succeed Diane Sawyer as ABC ‘World News’ Anchor

ABC News on Wednesday announced sweeping changes among its top news personalities, with Diane Sawyer to step down as anchor of the network’s evening newscast in August, replaced by David Muir, a rising star anchor at ABC. George Stephanopoulos, a co-host of “Good Morning America” and the host of the Sunday talk show “This Week,” will become the lead anchor for all breaking news coverage such as election nights.

The changes come as ABC News has mounted a wide-ranging challenge to NBC News as the ratings leader across numerous programs, having already topped NBC’s “Today” show as the dominant morning news program with “Good Morning America,” and edging past “Meet the Press” on Sundays with “This Week.”

Last month, the ABC nightly newscast, “World News” managed a rare win over NBC “Nightly News” among the viewers most desired by news advertisers, those between the ages of 25 and 54. (NBC still has a wide lead among total viewers in the newscast competition.)

ABC seems to be making an even more concerted effort to appeal to younger viewers with the appointment of Mr. Muir who is only 40 years old. The changes at the newscast had been expected for some time, with Ms. Sawyer, who is 68, moving on to the next step in her television news career.

ABC announced Wednesday that she would become a full-time anchor for investigative reports and major interviews. She will retain the title of ABC News anchor.

Mr. Muir has been a weekend anchor and chief substitute for Ms. Sawyer for some time as well as a lead correspondent for the network on major stories like the coverage of Hurricane Katrina. He also covered Mitt Romney in the last presidential election. He will become anchor of “World News” on Sept. 2. (He will also continue to anchor ABC’s magazine show “20/20.”)

Mr. Stephanopoulos, who has served as ABC’s chief political coverage anchor, will continue as anchor of both “Good Morning, America” and “This Week” on Sundays. His new title will be chief anchor of ABC News.

The dual appointments attempt to solve a much-speculated-on problem of who would succeed Ms. Sawyer by, in effect, giving part of her roles to Mr. Muir and Mr. Stephanopoulos.