President Joe Biden said he was praying for "the right verdict" in the trial of former Minneapolis Police Officer Derek Chauvin.
Telephoning George Floyd's family saying he and Vice President Kamala Harris: "We're all so relieved."
Chauvin was convicted of two counts of murder and one of manslaughter in the death of Floyd, a case that sparked a national reckoning on race and policing.
Biden said he hoped the verdict would give momentum to congressional police reform efforts saying the conviction "can be a giant step forward."
Floyd family attorney Ben Crump posting a video on Twitter of a phone call from Biden and Harris to the family.
Asked by a family member how he was doing, Biden said, "Feeling better now. Nothing is going to make it all better, but at least now there is some justice."
"This is a day of justice," Harris told the family after joining Biden to watch the verdict in the private dining room off the Oval Office.
Speaking hours ahead of the verdict, while the jury was deliberating in Minneapolis, Biden said he called Floyd's family the night before to offer prayers and could "only imagine the pressure and anxiety they're feeling."
"They're a good family and they're calling for peace and tranquility no matter what that verdict is," Biden said a few hours before the verdicts were announced.
"I'm praying the verdict is the right verdict. I think it's overwhelming, in my view. I wouldn't say that unless the jury was sequestered now."
Biden said he was only weighing in on the trial into the death of Floyd, who died with Chauvin's knee on his neck, because the jury in the case had already been sequestered.
The president has repeatedly denounced Floyd's death but had previously stopped short of weighing in on Chauvin's trial, with White House officials saying it would be improper to speak out during active judicial proceedings.
White House press secretary Jen Psaki repeatedly refused to explain Biden's comments, doing nothing to dispel the impression that he thought Chauvin should be found guilty.
Biden postponed planned remarks at the White House on his infrastructure package, once he found out a verdict was expected.
His comments came a day after Judge Peter Cahill, who presided over the trial, admonished public officials about speaking out.
"I wish elected officials would stop talking about this case, especially in a manner that's disrespectful to the rule of law and to the judicial branch and our function," he said shortly after sending the jury to begin deliberations.
Defence attorneys often cite remarks made by public officials as a reason to appeal a verdict, in part because they could poison the jury against the defendant.
Cahill delivered his rebuke after rejecting a defense request for a mistrial based in part on comments from California Rep. Maxine Waters, who said "we've got to get more confrontational" if Chauvin isn't convicted of murder.
He conceded to Chauvin's attorneys that Waters' comments could potentially be grounds for an appeal.
On Monday, Cahill ordered that jurors be sequestered in an undisclosed hotel during their deliberations and instructed them to avoid all news about the case.
Despite Cahill's remarks, Brock Hunter, a criminal defence attorney and past president of the Minnesota Association of Criminal Defense Lawyers, said he considered a successful appeal over remarks like Waters' and Biden's extremely unlikely.
"It's inevitable that public officials are going to comment on a case and its impacts on communities," he said. "Unless there is direct evidence that statements by a public official directly impacted a juror or jurors, I don't think this even gets off the ground."
Floyd's brother, Philonise Floyd, told NBC's Today show that Biden "knows how it is to lose a family member ... so he was just letting us know that he was praying for us and hoping that everything would come out to be OK."
On Capitol Hill, Republicans as well as Democrats said they were relieved at the verdict and predicted it could give momentum to policing reform legislation that has been proposed in both the House and Senate.
"I think the verdict just reinforces that our justice system continues to become more just," said Tim Scott of South Carolina, the only Black Republican senator. "This is a monumental day in many ways, in my opinion."
The Congressional Black Caucus watched the verdict together in the Capitol, and members hugged and fist pumped after the verdict was read.
"The room was filled with emotion and gratitude," said Georgia Rep. Hank Johnson. "Black lives mattered to this jury. And I'm very gratified at the verdict, very happy at the swiftness of the verdict. ... It's a vindication of justice in America."
House Speaker Nancy Pelosi joined the Black Caucus shortly afterward at a news conference outside, where she said she had spoken to Floyd's family just before the verdict.
She said she called "to say to them, 'Thank you, God bless you, for your grace and your dignity, for the model that you are appealing for justice in the most dignified way.'"
"Thank you George Floyd for sacrificing your life for justice," Pelosi said. "Because of you, and because of thousands, millions of people around the world who came out for justice, your name will always be synonymous with justice."
The verdict — and the aftermath — will be a test for Biden, who has pledged to help combat racism in policing, helping African Americans who supported him in large numbers last year in the wake of protests that swept the nation after Floyd's death and restarted a national conversation about race.
But he also has long projected himself as an ally of police, who are struggling with criticism about long-used tactics and training methods and difficulties in recruitment.