Playing the classic attack-dog role as Obama's running mate, Biden called the Republicans' presumptive nominee "a good family man" before going after him.
Romney has said "it's time to cut, cut back on teachers, firefighters and policemen," Biden told the crowd. "Not in my neighborhood."
The vice president was referring to remarks Romney made last month. What the former Massachusetts governor said was that Obama "wants another stimulus, he wants to hire more government workers. He says we need more firemen, more policemen, more teachers. Did he not get the message of Wisconsin? The American people did. It's time for us to cut back on government and help the American people."
Two spokesmen for the Romney campaign did not return requests for comment.
Biden also blasted GOP governors who have sought to roll back collective-bargaining rights for public employees - a clear reference to Wisconsin Gov. Scott Walker. "Did you think we would be fighting these fights again in 2012?" the vice president asked.
His remarks began loudly and passionately, but tapered off into a mellow, slow pace, as though he were having a fireside chat with the more than 3,000 members of the International Association of Fire Fighters in front of him in the Convention Center. He made three references, without elaborating, to the 1972 auto accident that killed his first wife and his daughter. He credited rescue workers with saving his two sons that day.
The president of Philadelphia's Local 22 firefighters' union, Bill Gault, said he was upset that Biden did not use the occasion to criticize Mayor Nutter's role in an ongoing contract dispute. The union is suing to prevent the city from appealing an arbitration award that would give firefighters three years of back raises and benefit increases.
"I'm disappointed the vice president didn't say, 'Yo, Mr. Mayor, honor our agreement,' " Gault said. "It's a very simple sentence."
Asked about Biden's statement that Republicans are the enemies of public employees, Gault said, "All politicians are the same to me right now."
Biden did make one Philadelphia reference, citing the two firefighters who died April 9 in a Kensington warehouse fire.
"I used to like the sound of bagpipes until I grew up," Biden said, before pausing for several seconds. "I don't like that anymore."
Several firefighters interviewed after the speech said they believed from the way Biden spoke that he understood their jobs and their challenges. He may have even swayed one Republican in attendance.
"I don't think a lot of the politicians get us," said Mike Devine, secretary-treasurer of a firefighters' union in Arlington, Va. But Biden "has gotten to know public safety."
As a Republican, Devine said, Biden's remarks "certainly puts a number of questions in your mind" about whom to vote for. Especially, he said, because he doesn't like Romney.
Contact Matt Katz at 609-217-8355, firstname.lastname@example.org, or follow on Twitter @mattkatz00.