Sawyer, 63, will be one of two women heading network newscasts, joining Katie Couric at CBS. The one time beauty queen from Kentucky has anchored CBS Morning News, served as a 60 Minutes correspondent and currently anchors ABC's Primetime Live and Good Morning America.
"Diane Sawyer is the right person to succeed Charlie and build on what he has accomplished," ABC News President David Westin told employees. "She has an outstanding and varied career in television journalism, beginning with her role as a State Department correspondent and continuing at 60 Minutes, Primetime Live, and Good Morning America."
Gibson, 66, took over the role in 2006, when he replaced the team of Bob Woodruff and Elizabeth Vargas. He will stay on through the end of the year.
"It has not been an easy decision to make," Gibson wrote in an e-mail to staffers. "This has been my professional home for 35 years.
World News currently ranks in the middle of the pack among the three networks, behind NBC Nightly News with Brian Williams, but well ahead of Couric's newscast.