Senate Majority Leader Harry Reid, D-Nev., said the Obama-Biden ticket will bring the change the country needs, including a filibuster-proof Senate majority.
Republican presidential candidate John McCain called Biden, his longtime Senate colleague and friend, to congratulate him, McCain campaign spokesman Tucker Bounds said. "It was a brief conversation. They've known each other for years," he said.
McCain's campaign wasted no time to try to turn the choice against Obama, producing an ad featuring Biden's previous praise for McCain and comments critical of Obama from an ABC News interview last year. Biden had said he stood by an earlier statement that Obama wasn't yet ready to be president and "the presidency is not something that lends itself to on-the-job training."
"Biden has denounced Barack Obama's poor foreign policy judgment and has strongly argued in his own words what Americans are quickly realizing -- that Barack Obama is not ready to be president," McCain campaign spokesman Ben Porritt said in a statement.
Some of Biden's Republican colleagues in the Senate praised the Delaware Democrat, including Sen. Richard Lugar of Indiana. Sen. Chuck Hagel, R-Neb., called Biden "the right partner for Barack Obama" and the decision "good news for Obama and America."
The Obama-Biden rally was set for old state Capitol where the Illinois senator kicked off his presidential campaign nearly 20 months ago. They were to be joined by Obama's wife, Michelle; Biden's wife, Jill; and the Bidens' three adult children, Hunter, Beau and Ashley.
A crowd of well-wishers waved to Biden and applauded as he left his home in Wilmington, Del., for a flight to Illinois just before noon EDT.
The Obama campaign sent a text message announcing his choice to supporters' phones and e-mail addresses about 3 a.m. EDT, the latest innovation by a tech-savvy operation that has deftly used the Web as a fundraising and organizing tool. The rollout was diminished somewhat when word of Obama's choice began leaking out to news media shortly before 1 a.m. EDT.
Obama and his famously disciplined team managed to keep Biden's selection a secret for several days, leading to a frenzy of speculation that mounted throughout the week. Two of those thought to be on the short list -- Virginia Gov. Tim Kaine and Indiana Sen. Evan Bayh -- indicated Friday night that Obama had chosen someone else.
Biden, 65, is a creature of Washington, a 35-year Senate veteran and chairman of the Foreign Relations Committee whose national security credentials will help patch a hole in Obama's relatively thin resume. Polls show that McCain holds a wide lead over Obama on the question of who is better prepared to be commander in chief.
Biden's straighforward style and working-class Catholic roots in Scranton, Pa., were also expected to help Obama appeal to middle- and working-class voters in battleground states like Ohio and Pennsylvania who favored Clinton in the primaries.
Officials close to Clinton said she was never formally vetted for the No. 2 position. The former first lady, who finished narrowly behind Obama in the primaries, will address the convention Tuesday night and her name will be placed in nomination even though she has endorsed Obama and has urged her delegates to support him.
"Sen. Biden will be a purposeful and dynamic vice president who will help Sen. Obama both win the presidency and govern this great country," Clinton said in the statement.
Biden has established a generally liberal voting record and a reputation as a long-winded orator. As a member of the Judiciary Committee -- he was its chairman from 1987 to 1995 -- he has played a key role in considering anti-crime legislation, Supreme Court nominees and constitutional issues.
While the war in Iraq has been supplanted as the campaign's top issues by the economy in recent months, the recent Russian invasion of Georgia has returned foreign policy to the forefront.
Biden was elected to the Senate at the age of 29 in 1972, but personal tragedy struck before he could take office. His wife and their 13-month-old daughter, Naomi, were killed when a tractor-trailer broad-sided her station wagon. Biden took his oath of office for his first term at the hospital bedside of one of his sons.
Biden dropped out of the 2008 race for the Democratic presidential nomination after a poor finish in the Iowa caucuses, but not before he talked dismissively of joining someone else's ticket.
He had stumbled on his first day in the race, apologizing for having described Obama as "clean." Months later, Obama spoke up on Biden's defense, praising him during a campaign debate for having worked for racial equality.
It was Biden's second try for the White House. The first ended badly in 1988 when he was caught lifting lines from a speech by British Labor Party leader Neil Kinnock.
