Chicago police estimate 800 to 1,000 activists gathered. There were no reports of arrests.
The protest began with a midday rally in Union Park as hundreds of people spoke out on issues ranging from immigration reform and corporate greed to the rising cost of healthcare and college.
"Student loans, they're really expensive, like at 6.8 percent," said college student Pablo Calderon. "That's higher than a mortgage at today's rates."
For weeks multiple groups of NATO summit protesters have been calling on people to descend on Chicago starting on May 1, but ABC7 saw few out-of-towners at Tuesday's event.
Curtis Gagnon, of Detroit, said he and a friend plan to return on NATO weekend.
"This is it," he said. "We need to stand up. This is the time. Let's do it. We're here, and look at them all. It's amazing how many people are here right now. I love it."
At one o'clock, the largely peaceful but vocal crowd took its message to the streets, heading east on Washington for the beginning of a two-mile march.
"The only solution is communist revolution," activists chanted.
"Stop complaining to your neighbors and get out here on the streets," protester Virginia Alvarez told ABC7. "There's more of us than there are of them. If everybody showed up, we'd turn things around."
May 1st rallies are an annual event, and recent demonstrations have been largely focused on immigration issues. But with the growth of the Occupy movement and the upcoming NATO summit, the year's event drew new people into the fray.
"I work at Ford and we work ten and a half hours a day, and we don't get any overtime until you work over 40 hours," said protester Calvin Jackson.
"I'm out here mainly for May Day and celebration of workers' rights," said Pete Dellos, protester. "Whether it's a warm-up for NATO for both us and the police, I don't really know."
At one point, protesters yelled expletives at the police, but officers did not respond.
"It's probably a good experience for some of the cops that are out here to warm up," said Supt. Garry McCarthy, Chicago Police Department. "I'm not going to call it a trial run, but we anticipate that it's going to be a good day. It's really that simple."
Protests were under way across the nation and the world Tuesday.
Occupy Chicago protests banks
Earlier Tuesday, upwards of five dozen protesters with Occupy Chicago sat down at the front doors of two Bank of America branches -- one on State, one on Washington, both in the Loop -- and for a short period neither branch had any visitors. The police, mostly bike patrol officers, set up their own lines in front of the banks.
There were no confrontations and no arrests.
"Occupy Chicago embraces the tactic of nonviolence," said a protester. "We believe that the only way to win our demands which are to put power back into the hands of ordinary people is to do so through a nonviolent method."
Supt. McCarthy was pleased with the way police handled Tuesday's protests.
"I saw cops taking it from people and they were showing a lot of patience and so those are the tactics that we take, and I like what I saw today from the department, and I feel pretty good about it," he said.
McCarthy said police training and a thin crowd contributed to the fact that there were no arrests or confrontations.
"I think our training is good, and I think, frankly, you know, it wasn't that big of a crowd so that certainly helped, but all in all, I think professional policing contributes to keeping the control," he said.