Former mayoral candidate Jesus "Chuy" Garcia threw his support behind Johnson, surrounded by several Hispanic leaders and elected officials at La Villita Community Church.
Garcia becomes the 5th former rival to take sides, which could provide a significant boost with a key group of voters.
"It's not a decision taken lightly, and I make it good standing with the best interest of the progressive movement and without any other hesitation or reservation. The choice is clear," Garcia said.
The U.S congressman, who finished fourth in the February run-off, is giving the Cook County commissioner a potential boost when it comes to Latinos who live on the Southwest Side and liberals who live on the lakefront.
Chicago mayoral debate turns heated as Vallas, Johnson discuss major issues
"His supporters are older -- perhaps so they probably have higher registration rates, they probably have a history more of turning up to vote," said Jaime Dominguez, a Northwestern University political science professor.
The former rivals came together to unite and close ranks in the progressive movement.
"Community development is at the center of everything that we want to do, investment in those communities, and we think that improves the quality of life in every aspect in public safety, housing and education, and all the things that everyone in every neighborhood want," Garcia said.
WATCH: Full ABC7 Mayoral Debate
Chicago Mayoral Debate: Brandon Johnson, Paul Vallas face off in ABC7 studios
"We are running on this movement to give our people a guarantee because that is what our people organize for," Johnson said. "That's what our people fought for and that's the dream that we're going to live. April 4 for Black and brown communities it's about to be lit in Chicago!"
Paul Vallas also got a key endorsement from the influential Chicago Laborers' District Council, which includes members in the construction, municipal and industrial sectors.
They said Vallas will prioritize infrastructure and encourage development.
Where does Chicago mayoral race stand after debate?
Where does Chicago mayoral race stand after debate?
Vallas in a hastily called news conference in response downplayed the impact of the endorsement turning the focus back to public safety
"I know I'm polling very well in the Latino community," Vallas said. "I anticipate that I'm going to poll very well are pulling also tells us that in the Latino community public safety is like the number one, two and three priority."
But as he frequently did during the ABC7 debate thursday, Vallas continued to raise the issue of Johnson's previous statements supporting defunding police.
"I want to restore public safety. My opponent want to further degrade an already degraded and demoralized police department. It's time to get serious about public safety if you want to be a serious candidate about mayor," Vallas said.
Johnson has said several times that he has no intention of de-funding the police.
"One we want to make sure that we are solving crime. You know, one of the deterrents to criminal activity is to catch people but we also have to focus on prevention," Johnson said.
Johnson also picked up the endorsement from the Reverend Jesse Jackson Friday afternoon.
Early voting begins this Monday.