Jennings was immediately seen as a rising star at ABC. The network was so confident in his abilities that Jennings was named one of the co-anchors of "ABC Evening News" in 1965. The stint would last for three years, part of which saw Jennings as sole anchor. But ABC's ratings never approached Walter Cronkite on CBS or Huntley-Brinkley on NBC and the attempt to pit Jennings' youthful, handsome good looks against the steadiness of ABC's rivals failed. Jennings has since said that he hated this period, was unprepared for the role and ill-at-ease.

After ABC changed formats, Jennings was "banished" to the network's Middle East Bureau, the first of its kind, where he thrived. Establishing the Beirut-based bureau as a rival to every other news gathering organization in the world, Jennings reported stories from virtually every Arab nation as well as Israel. He was on hand during the 1973 war, and, more importantly for ABC News, earned the respect of the viewers. The former dance show host had become a newsperson. In 1975, after Jennings did a few months as host of an ill-fated "A.M. America" (later given to the entertainment division and revamped as "Good Morning, America"), the network raised Jennings to chief foreign correspondent based in London. In 1978, when the network changed its evening newscast to "World News Tonight" and employed three anchors in three separate locations, Jennings was selected to handle the international coverage from London. When the attempt at multi-anchors did not catch on, Jennings was brought back to the US as sole anchor of the "World News Tonight" telecast in 1983, and was also named as senior editor of ABC News. Like Dan Rather at CBS and Tom Brokaw at NBC, Jennings would be ABC News' main star presence. By the end of the decade, Jennings' program often was the top-rated news show on the air, a feat ABC News had never previously achieved.

Combining a cool demeanor with a point-of-view enhanced by his international experience, Jennings has anchored three prime time specials on the Persian Gulf crisis (1991), hosted a town meeting which linked rivals Mikhail Gorbachev and Boris Yeltsin to America in an unprecedented question-and-answer session (1991), and has reported from all 50 US states as well as Bosnia-Herzegovina, Haiti and elsewhere. In addition to his other duties, he has anchored (and written) "Peter Jennings Reporting", a series of one-hour primetime specials investigating such issues as the abortion debate, the changing face of religion, the crisis of funding for the arts, and international hot spots. Jennings also hosted a series for PBS called "The AIDS Quarterly" (1990-91). As the ratings for "World News Tonight" rose, so did Jennings' acceptance with the critics. Often scoring better than Rather and Brokaw with the pundits, Jennings had been whispered to be pro-Arab in his views on the ongoing tensions between Israel and its neighbors. Partly this is due to reports that Jennings was married to a Palestinian. In fact, his second wife (of three) was Lebanese. Whatever his views on the Middle East or any other subject, like most news professionals aside from columnists, Jennings rarely expressed them publicly.

Jennings was the face of ABC News whenever a big story broke. He logged more than 60 hours on the air during the week of the Sept. 11, 2001, terrorist attacks, offering a soothing sense of continuity during a troubled time. His smooth delivery and years of international reporting experience made Jennings particularly popular among urban dwellers. When Tom Brokaw stepped down at NBC in November 2004, followed shortly by Dan Rather calling it quits at CBS due to a controversial reporting misstep,, ABC began an advertising campaign stressing Jennings' experience. But at a time when Jennings was poised to become the most familiar and seasoned network news anchor on the air, he announced in April 2005 that he was suffering from lung cancer. After a lengthy absence from the anchor chair, Jennings succombed to the disease in August 2005.