He was 58.
Russert had returned early from a family trip to Italy and was working at NBC's Washington bureau, recording voice-overs for Sunday's show, when he collapsed Friday afternoon. His wife, Maureen Orth, a writer for Vanity Fair, and their son, Luke, were still in Italy, where they had been celebrating Luke's graduation from Boston College.
"This news division will not be the same without his strong, clear voice," longtime NBC anchor Tom Brokaw said on MSNBC as he reported the news in a special report. "He will be missed -- as he was loved -- greatly."
"We cannot believe that he's gone, that we've lost his voice and that the country has lost this preeminent journalist," he added.
Russert's physician, Michael A. Newman, told MSNBC on Friday night that cholesterol plaque ruptured in an artery, causing sudden coronary thrombosis. An autopsy also revealed that Russert had an enlarged heart.
Shellshocked NBC News employees struggled with their emotions as they covered the death of the veteran political journalist, who had been a near-ubiquitous presence on MSNBC this year as he reported on the 2008 presidential campaign.
Speaking on MSNBC from Bagram Air Base in Afghanistan, where he is on assignment, anchor Brian Williams described Russert's death as "an unfathomable loss."
President Bush released a statement calling Russert "an institution," and condolences poured in from across the political establishment, over which the newsman exerted huge influence. As NBC News' Washington bureau chief, Russert shaped the network's political coverage, and his Sunday morning talk show helped frame the agenda for the coming week's news cycle.
His pronouncement last month that Sen. Barack Obama of Illinois would be the Democratic nominee heralded the end of the primary race, much to the dismay of the campaign of Sen. Hillary Rodham Clinton of New York.
On “Meet the Press,” which he had moderated since December 1991, Russert drew powerful guests who subjected themselves to his probing, as well as his practice of forcing them to confront their past statements, displayed on-screen.
"For almost a generation, he became the single most authoritative commentator on politics -- an accomplishment that will be hard for anyone to match any time soon," said Tom Goldstein, a journalism professor at UC Berkeley who knew Russert when they were both aides to New York politicians nearly 30 years ago.
On Sunday, Brokaw will host a special edition of "Meet the Press" that will serve as a retrospective of Russert's life.
Russert was an unlikely check on the politically powerful: the son of a sanitation worker who grew up in working-class Buffalo, N.Y., the first of his family to get a college degree.
Despite his encyclopedic knowledge of political history, Russert had an accessible, everyman approach on the air, famously scribbling "Florida, Florida, Florida" on a whiteboard early during the 2000 election night.
Friends said Russert was nearly giddy about covering this year's presidential race and its historic dimensions, working strenuous hours to keep up with the flood of news.
"I have never seen Tim more excited than he was about this campaign," said CBS' Bob Schieffer. "He just fed on it."
Timothy John Russert Jr. was born in Buffalo on May 7, 1950. His father worked two jobs, as a sanitation worker and a driver for the Buffalo News, to support the family. (In 2004, Russert published a book about his relationship with his father, "Big Russ and Me," one of two New York Times bestsellers he wrote).
Those who knew him said Russert's upbringing in heavily Irish, blue-collar South Buffalo left the newsman with a common touch that he never lost.
"Tim always would tell everybody that when he asked a question of a guest on 'Meet the Press,' he liked to think he asked a question that the guys at the American Legion would ask or understand," said Washington-based comedian Mark Russell, a fellow Buffalonian who graduated from the same Jesuit high school as Russert.
Russert studied political science at John Carroll University, a Jesuit school in Cleveland, before obtaining a law degree from Cleveland-Marshall College of Law.
He got his start in politics as a young field organizer for the 1976 Senate campaign of Daniel Patrick Moynihan (D-N.Y.). After working as Moynihan's chief of staff in the Senate, he signed on to Mario Cuomo's 1982 Democratic campaign for governor of New York and stayed with Cuomo as a counselor for two years.
In 1984, NBC News recruited him as a deputy to the news president. Initially, Russert worked behind the scenes, helping supervise the coverage of major events before being named Washington bureau chief in 1988. Three years later, then-NBC News President Michael Gartner asked him to be the new host of "Meet the Press."
Friends say he was unsure about making the move.
"He really reluctantly in the beginning came to television," said PBS anchor Judy Woodruff. "This isn't what he saw himself doing. But he found his way to combine his love of government and public policy, and to share the joy and curiosity and all the range of interests he had with an audience. So in a way, it was a natural."
Russert quickly helped lift the show from third to first place, a slot it has held the last decade. So far this season, the show has averaged 3.9 million viewers, while ABC's "This Week" has drawn 2.74 million and CBS' "Face the Nation" has pulled in 2.65 million, according to Nielsen Media Research.
"We reverted back to the original 'Meet the Press': Put a guest in the seat, turn on the lights, turn on the camera and go at it," Russert told the Kansas City Star last year. "Let people finish their thoughts, but be persistent."
Schieffer, who competed against Russert on Sunday mornings, praised him for making the transition from politics "in the way all of us in journalism can be proud of."
"He was not in any way partisan," he said. "He looked on everyone in the same way. He asked good, tough questions, and he asked them of everyone. His great secret was he listened to what someone had to say. You couldn't get one past him."
The NBC newsman's often-prosecutorial approach led his show to be dubbed the "Russert primary" by political aides; if candidates could survive an appearance on "Meet the Press," they had a shot.
Russert told the trade magazine TVWeek last year that he believed the show was an "oasis" on television.
"Most of the interviews you see are very quick, by the politicians' design," he said. "If you're able to get a public official or candidate to sit for an hour, you can really get beyond the boilerplate. . . . I think that can be an invaluable public service."
Russert was forced into the uncomfortable position of answering questions himself last year when he was called to testify in the federal perjury and obstruction trial of I. Lewis "Scooter" Libby, a former top aide to Vice President Dick Cheney. The newsman made no secret of his unease with the task, in which he testified that he had never spoken with Libby about the identity of CIA agent Valerie Plame, contrary to what Libby said.
Long an ambitious figure in the news division, Russert was once viewed as a contender to be president of NBC News but in recent years appeared content with his role. He had an unusually long contract with the network that guaranteed his spot on "Meet the Press" until 2012.
For all of his status in Washington, Russert was "not a very social animal," he told TVWeek. "I don't go to many dinner parties or cocktail parties. . . . I much prefer to go to a baseball game or basketball game with my son."
An observant Catholic, Russert was thrilled earlier this year when he was invited with a select group of journalists to meet Pope Benedict XVI during his visit to Washington.
Blitzer, also from Buffalo, recalls standing next to him in a small room at Catholic University, waiting for the pope to arrive. Russert was excitedly clutching his rosary and beaming.
"This wasn't Tim Russert, the powerful anchor and moderator of 'Meet the Press,' " Blitzer said. "It was just little Timmy from Buffalo. . . . He looked at me before the pope came in and said, 'Can you believe it, two kids from Buffalo are about to meet the pope?' "
Along with his wife and son, Russert is survived by his father and three sisters.
Times staff writers Meg James and Stuart Silverstein contributed to this report.