Biden's criticism was blistering of the defeated president whom he blamed for the assault that has fundamentally changed Congress and the nation, and raised global concerns about the future of American democracy.
"For the first time in our history, a president not just lost an election, he tried to prevent the peaceful transfer of power as a violent mob breached the Capitol," Biden said. "You can't love your country only when you win."
His voice booming at times, filling the ornate Statuary Hall where rioters had laid siege, the president called on Americans to remember what they saw Jan. 6 with their own eyes: the mob attacking police, breaking windows, a Confederate flag inside the Capitol, gallows erected outside threatening to hang the vice president - all while Trump sat at the White House watching it on TV.
"The former president's supporters are trying to rewrite history. They want you to see Election Day as the day of insurrection and the riot that took place here on January 6 as a true expression of the will of the people. Can you think of a more twisted way to look at this country, to look at America? I cannot."
The president's remarks launched the start of daylong remembrance, drawing a contrast between the truth of what happened and the false narratives that persist about the Capitol assault, including the continued refusal by many Republicans to affirm that Biden won the 2020 election.
"We must be absolutely clear about what is true and what is a lie," Biden said. "The former president of the United States of America has spread a web of lies about the 2020 election."
He said: "We are in a battle for the soul of America."
"I did not seek this fight, brought to this Capitol one year from today. But I will not shrink from it either. I will stand in this breach, I will defend this nation. I will allow no one to place a dagger at the throat of this democracy."
Republican leaders and lawmakers largely stayed away from the day's events, dismissing them as overly politicized - some continuing to spread false claims about the election.
From Florida, Trump showed no signs of letting go, and in fact revived his unfounded attack on the elections. He accepted no responsibility for egging on the crowd that day. Instead, in one of several statements Thursday, he said Biden was trying to "further divide America. This political theater is all just a distraction."
Even among congressional Republicans who condemned the attack in the days afterward, most have stayed loyal to the former president.
"What brazen politicization of January 6 by President Biden," tweeted Sen. Lindsey Graham, R-S.C., a sometimes Trump confidant. Others, including Senate Republican leader Mitch McConnell, were absent, with a contingent attending the funeral for a former colleague Sen. Johnny Isakson in Georgia. Far-right Reps. Marjorie Taylor Greene and Matt Gaetz stood by their refusal to certify Biden's election that day - "We're ashamed of nothing," Gaetz said on a podcast.
The division is a stark reminder of the rupture between the two parties, worsening since hundreds of Trump's supporters violently pushed past police, used their fists and flagpoles to break through the windows of the Capitol and interrupted the certification of Biden's victory.
Rep. Liz Cheney, chair of the House committee investigating the attack and one of the few GOP lawmakers attending the Capitol ceremonies, warned that "the threat continues." Trump, she said, "continues to make the same claims that he knows caused violence on January 6."
"Unfortunately, too many in my own party are embracing the former president, are looking the other way or minimizing the danger," she told NBC's "Today." "That's how democracies die. We simply cannot let that happen."
She was joined by her father Dick Cheney, the former vice president and now a respected Republican Party elder, who was greeted warmly by several Democrats. He stood with her, the only Republicans seen, for a moment of silence on the House floor.
He said in a statement: "I am deeply disappointed at the failure of many members of my party to recognize the grave nature of the January 6 attacks and the ongoing threat to our nation."
The Senate also convened a moment of silence.
Democrats investigating the insurrection plan to spend the coming months telling the American people exactly what happened last Jan. 6 with a series of public hearings.
Biden and his administration have come under criticism from some in his party for not forcibly explaining to Americans the ways democracy is at risk, or pushing Congress hard enough to pass election and voting rights legislation that is stalled by a filibuster in the Senate.
Barack Obama, the former president, said "nothing is more important" on the anniversary than ensuring the right to vote.
"While the broken windows have been repaired and many of the rioters have been brought to justice, the truth is that our democracy is at greater risk today than it was back then," Obama said in a statement.
Biden's address, and that of Vice President Kamala Harris who is leading the administration's efforts on the voting and elections legislation, appeared as a direct response to critics.
"We must pass voting rights bills," said Harris, addressing those gathered. "We cannot sit on the sidelines. We must unite in defense of our democracy."
On the House floor, where many members were evacuated and some were trapped as the rioters tried to break in, House Speaker Nancy Pelosi drew on history with a hope that Americans would turn to their "better angels" to resolve differences. She delivered private remarks to Hill staff who, as she told The Associated Press in an interview Wednesday, had stayed a year ago to "protect our democracy."
Biden's sharp message and the Republicans' distance from it come as lawmakers are adjusting to the new normal on Capitol Hill - the growing tensions that many worry will result in more violence or, someday, a legitimate election being overturned. Democrats and a handful of Republicans feel a desperate urgency to connect to a public in which some have come to believe Trump's lies that the election was stolen from him and that the attack wasn't violent at all.
A new poll from The Associated Press-NORC Center for Public Affairs Research showed that 3 in 10 Republicans say the attack was not violent, and about another 3 in 10 say it was somewhat violent. Around two-thirds of Americans described the day as very or extremely violent, including about 9 in 10 Democrats.
As Biden directed blame toward the former president, the percentage of Americans who blame Trump for the Jan. 6 riot has grown slightly over the past year, with 57% saying he bears significant responsibility for what took place.
In an AP-NORC poll taken in the days after the attack, 50% said that.
Trump's claims of widespread election fraud were rejected by the courts and refuted by his own Justice Department.
An investigation by the AP found fewer than 475 cases of voter fraud among 25.5 million ballots cast in the six battleground states disputed by Trump, a minuscule number in percentage terms.
Associated Press writers Darlene Superville, Kevin Freking, Jill Colvin Alexandra Jaffe and Farnoush Amiri contributed to this report.