DENVER | In a historic changing of the guard, Democrats formally anointed Sen. Barack Obama as America’s first black major-party nominee for president Wednesday night and bade farewell to the party’s two-decade domination by Bill Clinton and Hillary Rodham Clinton.
“Everything I learned in my eight years as president and in the work I have done since in America and across the globe has convinced me that Barack Obama is the man for this job,” Mr. Clinton told a thunderous, cheering crowd in a prime-time speech carefully scripted to end the rift between the two camps. “Barack Obama is ready to be president of the United States.”
The former president said Mr. Obama “hit it out of the park” with his first presidential decision of choosing Sen. Joseph R. Biden Jr. of Delaware for a running mate, and said the Obama-Biden ticket combines “experience and wisdom” along with “understanding, insight and good instincts.”
Mr. Biden, who is taking his shot at the White House after serving 35 years at the other end of Pennsylvania Avenue, accepted his vice-presidential nomination by paying tribute to the “common story” of modest roots that he and Mr. Obama shared growing up.
Laying the groundwork for an expected central theme in Mr. Obama’s speech Thursday night, Mr. Biden declared: “The choice in this election is clear. These times require more than a good soldier — they require a wise leader. A leader who can deliver change. The change everybody knows we need. Barack Obama will deliver that change.”
Mr. Obama arrived in Denver after days of campaigning, ready to accept his nomination with a speech Thursday night that is 45 years to the day that civil rights leader Martin Luther King gave his famous “I Have a Dream” address.
After Mr. Biden’s speech, Mr. Obama made a surprise visit on stage and paid tribute to the Clintons.
“President Clinton reminded us of what it’s like when you have a president who actually puts people first,” Mr. Obama said, in highlighting the former president’s address. He also told thrilled delegates that he was “so proud to have Joe Biden and Jill Biden and Beau Biden and Mama Biden and the whole Biden family with me on this journey to take America back.”
The Illinois Democrat learned in his hotel room earlier that the delegates had formally certified his nomination with a roll call cut short in a unifying move by his former rival, Hillary Rodham Clinton.
“In the spirit of unity with the goal of victory, with faith in our party and our country … let’s declare together in one voice right here and right now that Barack Obama is our candidate and he will be our president,” Mrs. Clinton said in honor of her one-time rival as some delegates wiped away tears and cheered wildly.
At 6:52 p.m. EDT, House Speaker Nancy Pelosi of California, the convention’s permanent chairman, declared “with great pride” that Mr. Obama would be the Democratic nominee.
“I have never seen a moment like this,” Rep. Artur Davis of Alabama said as Mr. Obama waited one more night to formally accept the nomination.
“I have never seen a sense of urgency like this,” he said. “In my 40 years, I have never seen my country as energized as this. As our next president has said, from the places where people hurt to the places where people dream, ‘Our time is now.’”
The official tally of delegate votes by all 55 states and territories is a quadrennial event, but this year it provided unusual drama. Some of the first lady’s supporters had threatened to use the event as a protest and it took some contentious negotiations between the two camps to secure a roll call that would let Mrs. Clinton’s backers celebrate her accomplishments one final time.
In the end, though, the vast majority of Democratic delegates stood behind their nominee as Mrs. Clinton had exhorted them a night earlier.
In one particularly poignant moment during the roll-call vote, Mrs. Clinton’s former home state of Arkansas gave all of its 47 votes to Mr. Obama. Rebecca Gwatney, the widow of recently slain Arkansas Democratic Party Chairman Bill Gwatney, lauded the Clintons for their contribution to the nation and their state.
She said Arkansas has “admiration for the Clintons that is unmatched throughout this country.”
“I’m proud tonight to follow Senator Clinton’s call for unity and to unite behind Senator Barack Obama and elect him the next president of the United States,” Mrs. Gwatney said.
Leading up to the New York vote, when the former first lady cut off the roll call, Mr. Obama had 1,249 delegates and Mrs. Clinton had 341. When Mr. Obama was formally nominated, the delegates cheered and danced to a song with the lyrics, “People of the world, join hands.” Many of them did.
The third night of the convention had a little bit of everything, from a wounded Iraq veteran who extolled the Democratic ticket’s national security credentials to the party’s failed 2004 nominee, Sen. John Kerry of Massachusetts, who delivered a withering attack on the Republican candidate, Sen. John McCain of Arizona, as a man who had lost his way.
“I have known and been friends with John McCain for almost 22 years. But every day now I learn something new about candidate McCain. To those who still believe in the myth of a maverick instead of the reality of a politician, I say, let’s compare Senator McCain to candidate McCain,” Mr. Kerry said.
“Let me tell you, before he ever debates Barack Obama, John McCain should finish the debate with himself,” he added.
Mr. Biden continued the attacks, repeatedly describing Mr. McCain’s policies and then declaring in cadence, “John McCain was wrong, Barack Obama was right.” The audience eventually picked up the chorus. He portrayed his running mate as the only option for changing America on issues as diverse as global warming, education, and diplomacy.
“You can learn an awful lot about a man campaigning with him, debating him, and seeing how he reacts under pressure. You learn about the strength of his mind. But even more importantly, you learn about the quality of his heart,” the Delaware Democrat told delegates.
“I watched how he touched people, how he inspired them, and I realized he has tapped into the oldest American belief of all: We don’t have to accept a situation we cannot bear. We have the power to change it.”
Florida delegate Andrew Gillum said he was excited about the new ticket. “I’m a huge Joe Biden fan for the same reason Barack Obama picked him: he’s strong, he’s fierce and he comes with the right set of credentials.”
A McCain campaign spokesman used the Clinton testimony to knock Mr. Obama, saying: “It is indicative of the concern among Democratic voters about Barack Obama’s inexperience that after three full days of the Democratic National Convention, President Clinton was finally forced to testify that Senator Obama is ready to be president, despite his previous arguments to the contrary.”
Mr. Clinton and his wife both criticized Mr. Obama on the primary stump as too inexperienced to be president, most specifically on foreign affairs.
The vice-presidential nominee followed an impassioned speech by Mr. Clinton, who shot down claims that Mr. Obama isn’t seasoned enough for the White House.
“We prevailed in a campaign in which the Republicans said I was too young and too inexperienced to be commander in chief. Sound familiar?” he said. “It didn’t work in 1992, because we were on the right side of history. And it won’t work in 2008, because Barack Obama is on the right side of history.”
Mr. Clinton praised Mr. McCain’s military record, but said he is pushing a failed policy adopted from President Bush.
“Let’s send them a message that will echo from the Rockies all across America. A simple message: Thanks but no thanks,” he said, to laughs and applause. “In this case, the third time is not the charm.”
Mr. Clinton, who at times during the primary expressed bitterness at the man who defeated his wife, was set to get out of town, leaving Thursday to the new nominee’s moment of glory.
During his speech, he made a humorous reference to the bitter primary of this spring.
“That campaign generated so much heat, it increased global warming. In the end, my candidate didn’t win. But I’m really proud of the campaign she ran,” he said, later, adding that Mrs. Clinton’s candidacy “tested and strengthened him.”
Republicans attempted to use Mr. Clinton’s expected absence from the Obama acceptance speech to stoke fires of disharmony, but a senior aide to the former president confirmed that he did not attend either the 2004 acceptance speech of Sen. John Kerry or the 2000 acceptance speech of his Vice President Al Gore.
A McCain campaign spokesman called Mr. Clinton’s testimony “indicative of the concern among Democratic voters about Barack Obama’s inexperience that after three full days of the Democratic National Convention, President Clinton was finally forced to testify that Senator Obama is ready to be president, despite his previous arguments to the contrary.”
Symbol and ceremony were everywhere on the floor. Mike Wilson, a Republican and Iraq veteran from Florida, was the first to nominate as the crowd chanted Mr. Obama’s name and his slogan, “Yes we can.”
Keeping with the unity theme, one-time Clinton supporter Rep. Debbie Wasserman-Schultz of Florida was one of the delegates to offer a speech to second the Obama nomination.
“No matter where we stood at the beginning of this campaign, Democrats stand together today,” she said to raucous applause. “We stand, united, proudly in our determination to elect Barack Obama.”
The same cohesion was heard in Clinton speeches.
“I stand with Hillary as she stands with Barack Obama to take our country back,” said Dolores Huerta, a union activist and delegate from California who nominated the former first lady.
The delegates paid tribute to Mrs. Clinton’s campaign.
“Women everywhere are inspired by my senator,” New York delegate Denise Williams Harris said in her nomination speech before the symbolic vote. “We cracked the glass ceiling 18 million times.”
The newly minted Obama-Biden ticket will leave Denver on Friday and begin a bus tour of economically troubled areas in Pennsylvania, Ohio and Michigan.
The “On the Road to Change” bus tour will stop first in Pennsylvania on Friday. It will mark the first joint campaign stumping for the senators since Mr. Biden’s selection was announced Saturday.
• Sean Madden and Sean Lengell contributed to this report.