Sen.would have to "figure out which of the seven kitchen tables to sit at" when considering his own economic future, said Biden, jabbing at the man he called his personal friend.
It was a reference to McCain's recent inartful admission - in a time of economic uncertainty - that he was not sure how many homes he owns.
"In his very first appearance as the vice presidential candidate, Biden demonstrated that he's more than willing to play the traditional role of attack dog," said CBSNews.com senior political editor Vaughn Ververs. "He recited a litany of what many Democrats feel is wrong with the current administration and linked his friend John McCain to them. In doing so, Biden proved himself an able fighter in his initial outing."
Before a crowd of more than 30,000 spilling out from the front of the Old State Capitol, Obama said Biden was "what many others pretend to be - a statesman with sound judgment who doesn't have to hide behind bluster to keep America strong."
Democrats coalesced quickly around the 47-year-old Obama's selection of the 65-year-old veteran of three decades in the Senate, a choice meant to provide foreign policy heft to the party's ticket for the fall campaign against McCain and the Republicans.
"The top advisers around Senator Obama over the last two weeks said to him, 'Look, we need to add heft to this ticket," reported CBS News chief Washington correspondent Bob Schieffer. "Every poll shows people like you but they do note you don't have experience. Biden adds heft to the ticket.' "
Obama made a symbolic choice for the site of the ticket's first joint appearance.
It was a brutally cold winter day more than a year ago when he stood outside the historic structure in the Illinois capital to launch his quest for the White House.
He returned this day in sunshine, the party's improbable nominee-in-waiting, a black man in his first Senate term who outdistanced a crowded field of far better-known and more experienced rivals for the nomination.
The Democratic National Convention opens on Monday to nominate him as president and Biden as vice president, the ticket that Democrats hope to ride into the White House after eight years of Republican rule.
McCain's convention opens on Labor Day. He has yet to select a running mate.
Responding to Obama's pick, the McCain campaign wasted no time trying to turn the selection to its own purposes.
It quickly produced a television ad featuring Biden's previous praise for McCain and comments critical of Obama. In an ABC 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.''
Polls indicate a highly competitive race at the end of a summer in which McCain eroded what had been Obama's slender advantage in the national surveys.
Obama brought Biden on stage with his glowing introduction to the strains of Bruce Springsteen's "The Rising."
The newly named running mate moved center stage in shirt-sleeves at a brisk trot that belied his 65 years, and embraced Obama.
"I'm glad to be here," said the man who has twice sought the presidency and emerged as Obama's pick only in the past few days.
Thousands of newly printed signs bearing the words Obama/Biden sprouted in the crowd that waited in anticipation in 90-degree temperatures.
Both men spoke for 16 minutes - unlikely a coincidence given Biden's reputation for verbosity.
Obama's remarks were carefully crafted to emphasize Biden's accomplishments in the Senate, his blue-collar roots and - above all - his experience on foreign policy.
"I can tell you Joe Biden gets it," he said. "He's that unique public servant who is at home in a bar in Cedar Rapids and the corridors of the Capitol, in the VFW hall in Concord, and at the center of an international crisis," he said.
Obama recounted the personal tragedy that struck Biden more than 30 years ago, within days of his election to the Senate, when his first wife and their child were killed in an automobile accident.
In a 1987 interview, Biden told CBS News he had to be convinced to take up his Senate seat, which he was sworn into at his son's hospital bedside, reports CBS News correspondent Kimberly Dozier.
"I didn't feel whole. I felt like a piece of me died," he said.
Obama said Biden raised his surviving children as a single parent, commuting between the Capitol and Delaware daily on the Amtrak train.
"For decades, he has brought change to Washington, but Washington hasn't changed him," Obama said, attempting to blunt an emerging Republican line of attack that notes Biden's 30 years in the polished corridors of the Capitol.
"He's an expert on foreign policy whose heart and values are rooted firmly in the middle class."
And when it comes to credibility on national security, Biden has a very personal connection to the issue of Iraq, reports Dozier - his son starts a national guard tour there later this year.
In a jab at McCain that foretold Biden's far sharper criticism, Obama said his political partner "will give us some real straight talk."
Biden offered parts praise for Obama and criticism of McCain.
"You can't change America and make things better for our senior citizens when you signed on to Bush's scheme of privatizing Social Security," he said.
"You can't change America and end this war in Iraq when you declare - and again these are John's words - 'No one has supported President Bush in Iraq more than I have,' end of quote. ladies and gentlemen, you can't change America, you can't change America when you know your first four years as president will look exactly like the last eight years of George Bush's presidency."
Obama was heading for Wisconsin while Biden returned to Delaware to prepare for the fall campaign.