It happened on Tuesday afternoon near 52nd and Thompson streets.
Adolphus Carr watched in horror before sprinting into action.
"I had to double park and run out and grab her and she was falling over," Carr said. "She was high as (expletive)."
Another good Samaritan, Damon Sedon, said the woman was in shock.
"She couldn't say anything and she almost dropped the baby," Sedon said.
Surveillance cameras show a group of good Samaritans rush to the aid of the 28-year-old mother, who police confirm was under the influence.
One man helped the mother to a bench, while another rocked the infant.
And when the wait for emergency responders took too long, the infant and her mother were put into a good Samaritan's car to get help.
"Not only did he flag down police for the 28-year-old mother, but he kept this two-month-old baby girl who he doesn't know. He transported the baby girl to a friend's house, and they did the right thing, they notified police," said Philadelphia Police Chief Inspector Scott Small.
"It was more so for the baby. The mom knows better, she shouldn't be doing that," said Sedon.
The mother was taken Lankenau Hospital and the infant was transported to Children's Hospital of Philadelphia.
Police confirm the child was never abandoned despite initial reports, and was never on a SEPTA bus.
Steven Gov, the manager of a laundromat near where the scene unfolded, said the handful of good Samaritans who came together showed that people do care.
"That was the most important thing, to get her out of the street, sit her down and just get her the help that she needed," said Gov.
Police have not filed any charges against the mother.