Wearing a black T-shirt printed with the words “I can’t breathe,” she lifted barrels of mayonnaise and enormous tins of tuna into her Restaurant Depot cart.

“Today is the first memorial for George Floyd,” she said quietly as she rolled the cart down the aisle.

She has not had much time to grieve lately, or even to rest.

Cannon-Grant, who is 39 and lives in Roxbury, organized the Tuesday march in Franklin Park that drew tens of thousands of people to protest police brutality and demand action in Boston. Though it followed on the heels of a protest that ended in violence downtown, she made clear that her march, which started with a “die-in” at Blue Hill Avenue, would be peaceful. And it was.

Cannon-Grant, who is at turns a firecracker and a mother bear, has also been distributing about 1,750 free meals a day, through the restaurant Food for the Soul in Dorchester, to people in the neighborhood who have struggled since the coronavirus hit. She is the mother of six children, two of whom she adopted as teenagers.

“Anything that goes down in the community, positive or negative, it almost has to go through Monica,” said Chris Lewis, a fellow activist who has known Cannon-Grant since they were children.

The two threads of Cannon-Grant’s work last week—feeding hundreds of people while at the same time agitating for specific policy prescriptions to end police brutality—help illustrate her overarching vision for change in the city. She has been inspired by the legacy of the Black Panther movement, she said, which challenged police violence while running massive “survival programs,” such as free breakfasts for school children that paved the way for the government’s free breakfast program.

Cannon-Grant’s focus, she and others said, is making sure the Black community in Boston can protect and serve itself.

“I studied a lot of the work that they did and how they were able to uplift and take care of their own communities,” Cannon-Grant said, sitting outside Food for the Soul as volunteers prepared free lunches inside. “My hope is to embody the Black Panther movement.”

In that spirit, Cannon-Grant hired her own security to keep the peace during the march in Franklin Park.

“I don’t have a relationship with the police department, and honestly I can’t depend on them to protect me. So I started reaching out to men in the community,” Cannon-Grant said. She offered them $100 to look out for instigators of violence and to de-escalate interactions with the police, which they did. In the end, around 50 Black men from the neighborhoods where the march took place acted as eyes and ears during it. They declined to be paid, she said.

Large numbers of people tend to follow her lead, said Donnell Singleton, the owner of Food for the Soul, who has worked with Cannon-Grant for years.

“Here’s Monica, with a sea of people behind her,” Singleton said of seeing her at Franklin Park on Tuesday.

Cannon-Grant has long been a thorn in the side of city and state politicians, urging them to take action to prevent violence against Black and brown people in Boston. She grew up in the Franklin Hill neighborhood of Dorchester, and attended the Jeremiah E. Burke High School.

It was wrong, she thought, that some politicians celebrated an overall reduction of violence in Boston, even as it continued in poor and majority-Black neighborhoods. After her teenage son twice had a gun pulled on him outside the family’s home, she decided enough was enough. She started attending every public safety meeting the city had, insistently pressing politicians on her central concern.

“They’re like, ‘Oh we’re doing great,’” she said. “So explain to me why my street is shot up 15 times and my son had a gun pulled on him twice? Why is this normal?”

Assisted by a source she won’t divulge, she began posting almost every shooting or stabbing that took place in the city on her Facebook page with the hashtag #ViolenceinBoston in 2017. That also became the name of the nonprofit she launched that year, to provide direct resources like food and housing to Black and brown victims of violence in Boston.

If she didn’t post quickly enough, bystanders or those involved in shootings would send her Facebook messages to let her know what happened. “Shots fired outside my house … 2 shots in my driveway,” read one message she received last month.

“There’s been many a night, late at night, that I get a call from Monica and there’s a crime scene that she’s telling me to meet her at,” said former city councilor Tito Jackson, one of Cannon-Grant’s mentors and close friends.

As someone without a college degree or institutional affiliations, Cannon-Grant and her peers felt she was often dismissed by elected officials and others in power as not having much to add. And so she took to inviting herself, being so persistent and sometimes disruptive that she couldn’t really be ignored.

Beginning in 2018, she launched a nearly yearlong campaign to get Mayor Martin J. Walsh to meet with her. She called him out on Twitter and blasted him on Facebook Live videos; in a typical post from October 2018, she wrote, “Today makes 99 days since Mayor Marty Walsh called my cell phone agreeing to meet with me. Last night Boston’s 47th Homicide…He loves press conferences to give the perception he’s doing something but he’s not.” She was particularly outraged by comments he made in July 2018 addressing shooting victims in Dorchester, which she thought blamed them for the violence they suffered.

“If you want to kill each other — it’s a horrible thing and I don’t want to stand here as mayor and say, ‘You know, we’re justifying that’ — you kill each other,” Walsh said at the time.

Finally, after what Cannon-Grant described as “256 days of advocacy,” Walsh met with her. Sharing a plain bagel at Soleil, they cut right to the chase.

“Can you stop calling me a motherf*****?” Cannon-Grant recalled Walsh asking at the beginning of the meeting.

“I said, ‘Sure, I need you to also stop getting in the media, talking about Black men in the community as if you actually understand what it is to be a Black man.’”

Then the two had an honest conversation, both said in interviews, one that opened up an avenue for them to work together. Walsh said he had made comments out of frustration and concern at seeing people dying day after day.

“And I told him I feel the same way and since then, we’re aligned in our frustration,” Cannon-Grant said. “You’re supposed to disagree, you’re supposed to have conversations and then figure out how you could work together.”

The mayor has since directed funding and resources to Violence in Boston, as well as the Food for the Soul project.

“We certainly weren’t mortal enemies, but there was definitely a lot of conflict there and barriers to communication,” Walsh said in an interview. “And that hour — maybe a little longer — broke down those barriers.”

The story of her evolving relationship with Walsh over the past two years is also the story of her own changing role in the city, from that of a marginalized activist beating down the walls of those in power, into someone who wields significant power and influence on behalf of her community.

“A lot of what she was acting out on at first was her own pain,” said Thaddeus Miles, director of community services at MassHousing. Now, he said, “She’s more strategic around her thought and she’s worked with her allies in a different way.”

As a sign of her growing stature both in the city and beyond, she hosted a town hall last week that featured Senator Elizabeth Warren, Representative Ayanna Pressley, and Emerald Garner, a daughter of Eric Garner, a Black man who died after being placed in a chokehold by a police officer in New York. The group discussed how to pass federal legislation mirroring state legislation targeting police brutality, including a California law banning the use of deadly force by police if there is a reasonable alternative, and a New York bill requiring that police provide medical help to those in custody who request it.

Cannon-Grant ran for state representative in 2016 and lost. Then in 2017, she organized the Fight Supremacy rally on the Boston Common the week after a white supremacist march in Charlottesville, Va. Politicians and even other activists at the time worried that it wasn’t a good idea, Miles said — that she didn’t have the organization to pull it off. They feared it would disintegrate into a violent clash between white supremacists and protesters.

That didn’t happen. Instead, she drew tens of thousands of people to the Boston Common for a peaceful march.

“People started to take her seriously,” said Miles.

But even with increased recognition, Cannon-Grant continues to agitate when she deems it necessary.

In one notable example from 2019, she interrupted a panel featuring Governor Charlie Baker, Attorney General Maura Healey, and House Speaker Robert DeLeo in the wake of the school shooting in Parkland, Fla. The panel was meant to assess how Massachusetts had achieved such a low rate of deaths from guns.

“I’m sorry but there are Black and brown folks sitting in this room that I brought with me who are victims of gun violence in Black communities that get ignored every day,” Cannon-Grant said from the darkened audience. “No disrespect, but we were screaming way before Parkland.”

She then brought her own chair onto the stage, filled mostly with white men in suits, and began taking questions from the audience.

Anne Grammer, the 82-year-old cofounder of Cape Cod Grandmothers Against Gun Violence, was so moved by Cannon-Grant’s words that, a few weeks afterward, she drove to Cannon-Grant’s house and offered to volunteer for her.

“Anything she asked me to do, I will do,” Grammer said.

Cannon-Grant credits her fighting spirit to her grandmother, who worked the polls and was the head of her tenant association in Boston for many years.

“My grandmother was a fighter,” Cannon-Grant said, laughing. “She would invite the city councilors to the cookout to curse them out about what they didn’t do for the community.”

That’s how onlookers describe Cannon-Grant, too.