Russert, 58, was a political operative before he was a journalist. He joined NBC a quarter century ago and ended up as the longest-tenured host of the Sunday talk show "Meet the Press."
He was an election-night fixture, with his whiteboard and scribbled figures, and was moderator for numerous political debates. He wrote two best-selling books, including the much-loved "Big Russ and Me" about his relationship with his father.
He was NBC's Washington bureau chief.
President Bush, informed of Russert's death while at dinner in Paris, saluted him as "a tough and hardworking newsman. He was always well-informed and thorough in his interviews. And he was as gregarious off the set as he was prepared on it."
NBC interrupted its regular programming with news of Russert's death and continued for several hours of coverage without commercial break. The network announced that Tom Brokaw would anchor a special edition of "Meet the Press" on Sunday, dedicated to Russert.
Competitors and friends jumped in with superlative praise and sad recognition of the loss of a key voice during a historic presidential election year. Known as a family man as well, he had been named Father of the Year by parenting organizations.
Familiar NBC faces such as Brokaw, Andrea Mitchell and Brian Williams took turns mourning his loss.
Williams called him "aggressively unfancy."
"Our hearts are broken," said Mitchell, who appeared emotional at times as she recalled her longtime colleague.
CBS News chief Washington correspondent Bob Schieffer, Russert's competitor on "Face the Nation," said the two men delighted in scooping each other.
"When you slipped one past 'ol Russert, you felt as though you had hit a home run off the best pitcher in the league," he said. "I just loved Tim and I will miss him more than I can say."
In a blog post CBS Evening News anchor Katie Couric wrote, "He was a big teddy bear of a guy. But he was also a pit bull of an interviewer. He always held people's feet to the fire, often using their past words with great effect to reveal a flip-flop or hypocrisy. While he was incredibly tenacious, he always did it with great humanity and respect
Russert developed a style that was unique and effective, commonly confronting his guests with past quotes that differed from their current positions and staying on a single point until he received an answer, writes.
He was also a senior vice president at NBC, and this year, Time Magazine named him one of the 100 most influential people in the world.
Russert had Buffalo's blue collar roots, a Jesuit education, a law degree and a Democratic pedigree that came from his turn as an aide to the late Sen. Daniel Patrick Moynihan of New York.
One of his books, "Big Russ and Me," was about his relationship with his father, who was a garbage collector.
The young Russert helped him haul garbage during the summers and his father helped him as the source of his values and the source of one of his greatest ideas, reports CBS News correspondent Richard Schlesinger. On election night in 2000, he made history by tracking one of the closest elections ever on plane white boards. It was, Russert said, inspired by his father who gave him advice every reporter if not every politician follows: keep it simple.
"He taught be more by the quiet eloquence of his hard work, his basic decency, his intense loyalty. He taught me the true lessons of life," Russert said in 2007.
He was married to Maureen Orth, a writer for Vanity Fair Magazine. The couple had one son, Luke. According to MSNBC.com, Russert met his wife at the 1976 Democratic National Convention.
Praise flowed quickly from those who knew Russert across the television interview room.
"It was Tim's great gift to combine civility with tough-minded, relentless probing of a public figure's ideas and policies," said CBS News senior political correspondent Jeff Greenfield said. "He rarely if ever let the canned talking points go unchallenged. He invented the technique of putting the subject's words on the table, and insisting on pushing the guest into attempting to square the circle. He was as good as it gets."
Senate Majority Leader Harry Reid said Russert was "the best in the business at keeping his interview subjects honest."
"There wasn't a better interviewer in television," Sen. Barack Obama, the Democratic presidential contender, told reporters in Ohio.
Republican Sen. John McCain of Arizona, Obama's rival for the White House, hailed Russert as the "pre-eminent journalist of his generation."
Rep. John Boehner of Ohio, the House Republican leader, said Russert was "one of the smartest, toughest television news journalists of all time .... I can say from experience that joining Tim on Meet The Press was one of the greatest tests any public official could face."
Carl P. Leubsdorf, president of the Gridiron Club, an organization of journalists, said in a statement, "It was a measure of the degree to which Tim Russert was respected in the journalistic world that he was the first broadcaster elected to membership in the Gridiron Club after the rules were changed in 2004 to end our century-old restriction to print journalists."
"He was an enthusiastic member and a willing participant in our shows. His fellow Gridiron members join with all of those who knew and respected Tim in mourning his untimely death."
"Tim will be sorely missed because his years as Senate staffer and probing TV journalist gave him special insights on political and governmental issues," said Sen. Arlen Specter, R-Pa. "Had he chosen law as a career, his cross-examination would have made him a star in that field as well."
"It is my sad duty to report this afternoon" that Russert collapsed and died while working in the network's Washington studios,
"He'll be missed as he was loved greatly," Brokaw said.
Russert had dozens of honorary college degrees, and numerous professional awards.
He won an Emmy for his role in the coverage of President Ronald reagan's funeral in 2004.