Rallies were held in cities from New York to Oakland and stretched into the South, historically difficult territory for organized labor.
The striking workers say they want to unionize without retaliation in order to collectively bargain for a "living wage."
They are demanding $15 an hour, more than twice the federal minimum of $7.25. The median wage for front-line fast-food workers is $8.94 per hour, according to an analysis of government data by the National Employment Law Project (NELP), an advocacy group for lower-wage workers.
"It's almost impossible to get by (alone)," said McDonald's worker Rita Jennings, 37, who was among about 100 protesters who marched in downtown Detroit Thursday. "You have to live with somebody to make it."
Jennings said that in her 11 years at McDonald's, she has never received a raise above her wage of $7.40 an hour.
In Atlanta, about 20 fast-food workers at two different chains presented their managers with "strike letters" before walking out, Roger Sikes, a coordinator with the nonprofit group Atlanta Jobs With Justice, told Reuters.
And in Oakland, about 80 fast-food workers from various restaurants and their supporters rallied outside a Kentucky Fried Chicken outlet.
"I'm doing it for the respect for myself and for my other coworkers," said Ryan Schuetz, 20, who works at McDonald's. He said his work hours have been reduced recently and that he was struggling to keep a roof over his head.
Several politicians came out in support of the protesters on Thursday.
In New York City, mayoral candidate and City Council Speaker Christine Quinn joined several hundred demonstrators outside a McDonald's in midtown Manhattan, holding a sign that read "On Strike: Wages Too Damn Low."
"Better pay will put more money into local businesses and spur economic growth," Democratic Representative George Miller of California said in a statement.
Robert Hiltonsmith, a policy analyst at Demos, a liberal think tank, said that if the minimum wage had kept up with productivity and inflation, it would be closer to $17 per hour.
He added that in many cases, low pay wasn't justified by a worker's lack of marketable skills.
"Seventy percent of these fast-food workers are aged 20 or over, so they're not teenagers, and of that 70 percent, about a third of them have college degrees," he said.
"So it's not that they don't have skills - in many cases, the jobs aren't there for them."
Momentum Building
Thursday's demonstrations in 60 cities followed several smaller strikes this year in the $200 billion U.S. fast-food sector, organizers said.
Last November, some 200 workers walked off their fast-food jobs in New York City, and groups in Chicago, Kansas City, Detroit and other cities followed their lead in April and July.
Fast-food wage activists are now receiving financial and technical support from the Service Employees International Union (SEIU).
Their active online presence echoes Occupy Wall Street - a movement that several supporters of the protests cited as an inspiration.
Restaurant chains and trade groups say the protests are unwarranted because fast-food and retail outlets provide Americans with millions of good jobs with competitive pay and ample opportunities to rise through the ranks.
"Our history is full of examples of individuals who worked their first job with McDonald's and went on to successful careers both within and outside of McDonald's," the company said in a statement.
In an emailed statement, Burger King said the company respects the rights of its workers but "does not make hiring, firing or other employment-related decisions for our franchisees."
The restaurant chains have not changed their wage policies despite the recent strikes.
The National Retail Federation called the strikes "further proof that the labor movement (has) abdicated their role in an honest and rational discussion about the American workforce."
And in the Wall Street Journal on Thursday, the conservative Employment Policies Institute ran a full-page ad with a picture of a robot making pancakes, warning that higher wages would mean "fewer entry-level jobs and more automated alternatives."
"You can either raise prices and lose customers, or (automate) those jobs," said Michael Saltsman, EPI's research director. "The idea that restaurants are rolling in the money is not representative of the situation franchisees face."
Dorian Warren, an assistant professor of political science at Columbia University who has published work on labor organizing and inequality, said new protests in the South are "a huge, huge deal."
"The South has always been the model for low wage employment, from slavery to the Jim Crow laws, to the present. It's also the most anti-union part of the country, so the fact that workers feel empowered enough to take collective action is enormous," he noted.
