The co-anchors will make their debut Jan. 3 -- the same time "World News Tonight" becomes the first evening newscast to deliver live versions to both the East and West Coasts, ABC News President David Westin announced.
Woodruff, who has been the anchor of "World News Tonight" weekend editions said he was "honored and humbled" by the appointment.
"Peter Jennings set a standard that all of us in journalism aspire to meet," he said. "Following in his path as co-anchor of this broadcast is a weighty challenge but it's also an opportunity for Elizabeth and me to help ensure the broadcast lives up to his ideals and continues his unwavering commitment to covering the world."
In addition to the live network feeds, Vargas and Woodruff will also produce live daily Webcasts starting Jan. 3 for ABC News Now, ABCNEWS.com and to be distributed wirelessly.