The protester was Ute Schmid-Jones, who ran for the Green Party of Canada in the 2015 federal election.
Schmid-Jones shoved past reporters screaming, "Keep your promises," and throwing pumpkin seeds with hearts drawn on them as Trudeau was leaving city hall.
The prime minister was ushered into a waiting SUV while Schmid-Jones was forced to the ground by security, as she repeatedly yelled, "Don't hurt me!"
Hamilton police said she has been released and isn't currently facing any charges, but also that the matter is an "active investigation."
Green Party press secretary Dan Palmer told CBC News that Schmid-Jones is "still currently a member of the party," but that she "holds no formal role or title.""We strongly condemn that sort of behaviour," Palmer said, adding that the party "absolutely supports her being held to account by local authorities."
Schmid-Jones told CBC News that she was protesting to get the word out about pipeline issues in the Hamilton area.
"We don't want a pipeline, Line 10, built here in Hamilton," she said.
The National Energy Board is currently holding hearings in Hamilton for the Enbridge Line 10 replacement project, which includes a proposal to expand the size of a section of a pipeline that runs through Hamilton.
Schmid-Jones can be seen in photos alongside Green Party of Ontario Leader Mike Schreiner at a Hamilton 350 rally outside the NEB hearing in Hamilton on Tuesday.
She said that she "tossed" the seeds at Trudeau, with the intent to "give the prime minister some pumpkin seeds when he passed."
"I expected to be escorted away, but I did not expect to be tackled," she said. After she was taken from the scene, Schmid-Jones says she was "grilled for two hours straight" about her affiliations, and why she did what she did.
"I did it because I care, and I didn't know how else to get my point across," she said. "It was my action. I chose to go this route independently."
Schmid-Jones also said that she was "treated with respect by the people who questioned her."
"I am grateful for their professionalism," she said. Though she is not currently facing charges, Schmid-Jones says she is now banned from Hamilton City Hall.
Trudeau made two stops in Hamilton on Friday, one of which was at city hall to meet with Mayor Fred Eisenberger.
"The close working relationship that we've established with mayors like you right across the country is really important when it comes to actually making the investments that are going to help citizens get to and from work, find good housing, and be resilient against the changes to our climate," the prime minister said.
Trudeau's visit with the mayor gave Eisenberger a chance to convey Hamilton concerns, like the unease felt by pensioners owed benefits by U.S. Steel Canada, formerly Stelco, the mayor told reporters after the meeting.
"The primary concern is the pensioners," Eisenberger said.
Trudeau didn't get into detail on the campaign trail over the so called "secret deal" allowed by the previous federal government with U.S. Steel, but did criticize what he called the Conservatives' approach to making "decisions around foreign investment based on case-by-case, back-of-the-napkin political concerns rather than what truly is in the best interest of Canadians."
Eisenberger said he and Trudeau did not discuss unsealing that deal. "I'd rather focus on how we go forward," the mayor said.
Eisenberger said he also talked about poverty and affordable housing in Hamilton, as well as the city's infrastructure needs. "I did mention that LRT is moving forward quickly," he said.
Trudeau also met with the members of Hamilton city council, who gleefully posed for pictures with the prime minister.
The prime minister scheduled three photo-ops in town before heading on to St. Catharines and Port Colborne Friday afternoon.
He visited Picone's Fine Foods in Dundas after his stop at city hall, where politicians on the campaign trail have often gone to get pie.
After he leaves Hamilton, the prime minister is expected to stop at vegan doughnut hot spot Beechwood Doughnuts in St. Catharines and then head on to Port Colborne.