The 68-year-old - who also acts as managing director - has handed her position over to David after 5 years in the role.
David, 40 - who currently anchors the weekend edition of 'World News' - has filled in as a substitute anchor for Diane in the past and is all set to assume the position following her departure this August.
The ABC reporter took to Twitter to express his excitement and said he felt ''humbled'' but ''honoured'' by the appointment.
He wrote on the social networking site (25.06.14): ''This is an incredibly humbling day. Honored to join @DianeSawyer and @GStephanopoulos in this great new adventure [sic]''
News of a shake-up amongst the anchor team first broke earlier this year when former 'Good Morning America' presenter Diane announced she would be changing roles at the channel.
She said: ''After wonderful years at 'World News' I decided it is time to move to a new full time role at ABC News.''
ABC News president James Goldston also paid tribute to her through a press release.
He wrote: ''For many years to come Diane will be a driving force at ABC News with her exceptional storytelling genius. She is one of the giants of modern journalism. Her curiosity, passion and energy are unmatched, and I can't wait to see where she'll lead us next.'
The renowned journalist will be taking on the role left by recently-retired Barbara Walters at the broadcasting company, hosting specials, conducting big name interviews and covering investigations.