Warren, the Harvard professor who's locked in a tight battle with Republican Sen. Scott Brown, said she and President Obama are on the side of small business owners.
"People feel like the system is rigged against them. And here's the painful part: they're right," she said.
"Oil companies guzzle down billions in profits. Billionaires pay lower tax rates than their secretaries. And Wall Street CEOs--the same ones who wrecked our economy and destroyed millions of jobs--still strut around Congress, no shame, demanding favors, and acting like we should thank them."
As for small business owners, Warren added, "Not one of them--not one--made big bucks from the risky Wall Street bets that brought down our economy."
"I talk to nurses and programmers, salespeople and firefighters--people who bust their tails every day. Not one of them--not one--stashes their money in the Cayman Islands to avoid paying their fair share of taxes," Warren continued, alluding to Democratic accusations that Romney is stashing some of his wealth in offshore accounts.
She also accused Romney of wanting "to give tax cuts to millionaires and billionaires...but for middle-class families who are hanging on by their fingernails? His plans will hammer them with a new tax hike of up to $2,000."
"Mitt Romney wants to give billions in breaks to big corporations - but he and Paul Ryan would pulverize financial reform, voucher-ize Medicare, and vaporize Obamacare," she added.
"After all, Mitt Romney's the guy who said corporations are people. No, Governor Romney, corporations are not people. People have hearts, they have kids, they get jobs, they get sick, they cry, they dance. They live, they love, and they die. And that matters. That matters. That matters because we don't run this country for corporations, we run it for people," Warren said.
Warren's high-profile, prime time appearance at the convention just prior to former President Bill Clinton serves two purposes: to fight back against Republican attacks, especially their continued use of the president's "you didn't build that" line, and to boost her profile for the final stretch of her Senate campaign.
"President Obama believes in a level playing field," she said. "He believes in a country where nobody gets a free ride or a golden parachute.
"A country where anyone who has a great idea and rolls up their sleeves has a chance to build a business, and anyone who works hard can build some security and raise a family," she added.
"President Obama believes in a country where billionaires pay their taxes just like their secretaries do."