ABC broke the news with a special report Sunday night.
"Peter died with his family around him, without pain and in peace. He knew he'd lived a good life," his wife and children said in a statement, according to ABC.
"For four decades, Peter has been our colleague, our friend, and our leader in so many ways," wrote ABC News President David Westin in a message to ABC employees. "None of us will be the same without him."
On Monday, colleagues, fans and national leaders also paid tribute to Jennings and his career.
"Peter Jennings had a long and distinguished career as a news journalist. He covered many important events, events that helped define the world as we know it today," said President Bush in a statement. "A lot of Americans relied upon Peter Jennings for their news. He became a part of the lives of a lot of our fellow citizens, and he will be missed. May God bless his soul."
Secretary of State Condoleezza Rice called Jennings "a close personal friend" and said he "represented all that was best in journalism and public service. A man of conscience and integrity, his reporting was a guide to all of us who aspire to better the world around us. I learned from him and was inspired by him."
Former rival Tom Brokaw of NBC said "we were not just competitors and colleagues. We were really friends. We had a lot of opportunities to reflect on this in the last year. ... It was a competitive brotherhood."
Jennings was born in Canada and dropped out of high school to become a broadcaster. Largely self-educated, Jennings' on-air confidence and good looks quickly catapulted him to prominence. He was appointed the top ABC news anchor host of "Peter Jennings with the News" in 1965 -- at 26 years old. Some critics derided the network for choosing good looks over substance and experience in their approach to the news.
Toward the end of that first stint as a national news anchor, the then callow Jennings realized he needed more training as a journalist.
"I did it for three years," Jennings told NPR in a 1998 interview. "For the first two years I was too stupid to feel awkward about it."
In 1967, Jennings asked to be assigned to the field as a reporter in order to gain more experience.
For the next two decades, Jennings reported from the Middle East, Rome, London and many other international locations. His early field reporting combined with later location reports as an anchor made him witness to and an authority on some of the world's most significant news events.
"He was in Berlin in the 1960s when the Berlin Wall was going up, and there in the '90s when it came down," ABC News reported Monday. "He covered the civil rights movement in the southern United States during the 1960s, and the struggle for equality in South Africa during the 1970s and '80s. He was there when the Voting Rights Act was signed in the United States in 1965, and on the other side of the world when black South Africans voted for the first time."
During his 40-year career, Jennings also covered the Vietnam war, the Munich Olympics hostage crisis, genocide in Cambodia and rise of democracy movements in Eastern Europe. He reported from every U.S. state and from locations around the globe. He established the first American news bureau in any Arab country when he opened ABC's Beirut, Lebanon bureau in 1968. In the 1970s Jennings served as the network's chief foreign correspondent and as its international anchor.
In 1983, Jennings took over as sole anchor for World News Tonight, where, among other things, he is credited with keeping international news on network television. He also was a part of what the New York Times called the "the era of the television news anchor as lavishly compensated, globe-trotting superstar." Jennings and his colleagues and rivals Dan Rather of CBS and Brokaw of NBC became evening news fixtures for much of the 1980s and 1990s.
Jennings went on location to cover the 1991 Gulf War and again recently for the ongoing Iraq war.
Jennings' anchored coverage of the new millennium celebrations from New Year's Eve 1999 to New Year's Day 2000 won his network a Peabody award. He stayed on the air for 25 hours straight.
He later drew on that experience when he stayed on the air day after day following the Sept. 11, 2001 attacks, logging some 60 hours of live anchor work during and after the events of the day, a feat that many colleagues called "superhuman."
Many tributes and obituaries have commented on Jennings' smooth and authoritative style in the anchor chair.
"His well-rounded tones, world-savvy air and matter-of-fact delivery led World News Tonight to the top of the ratings for 11 of the past 20 years," wrote Patricia Sullivan in the Washington Post.
Colleague Ted Koppel compared him to actor Roger Moore, who portrayed suave British secret agent James Bond.
But all of Jennings' colleagues also paid tribute to his journalistic skill.
"Inside that tall, handsome, elegant and eloquent exterior -- inside that beat the heart of a fierce, but principled competitor," said Rather of CBS. "The last person you wanted to see coming on a story, particularly a big story, was Peter Jennings. ... How much did I keep an eye on him? Constantly. All the time."
In 2003, citing a long love of the United States and the traumatic events of Sept. 11, Jennings became a U.S. citizen while retaining his Canadian citizenship.
"Not to sound too corny about it, but love, respect, gratitude, time," Jennings told the Associated Press, when asked his reasons for making the move. "I've been thinking about this for so long. This is not the kind of thing you can do overnight."
Jennings announced the diagnosis of his disease and left his role as ABC news anchor in April, saying he hoped to recover and return to work.
He had reportedly given up smoking about 20 years ago, but started again around the time of his marathon Sept. 11 coverage. Reports said he had quit smoking again at some point before his diagnosis.
According to ABC News, Jennings was awarded 16 Emmys, two George Foster Peabody Awards, several Alfred I. duPont-Columbia University Awards and several Overseas Press Club Awards.