Petry's desire to become a professional writer was raised first in high school when her English teacher read her essay to the class and commented on it with the words: "I honestly believe that you could be a writer if you wanted to." The decision to become a pharmacist was her family's. After graduating in 1929 from Old Saybrook High School, she went to college and graduated with a Ph.G. degree from the University of Connecticut College of Pharmacy in New Haven in 1931 and worked in the family business for several years, while also writing short stories. On February 22, 1938, she married George D. Petry of New Iberia, Louisiana, and moved to New York. She worked as a journalist writing articles for newspapers including The Amsterdam News (between 1938 and 1941) and The People's Voice (1941–44), and published short stories in The Crisis, where her first story appeared in 1943, Phylon, and other outlets. Between 1944 and 1946 she studied creative writing at Columbia University. She also worked at an after-school program at P.S. 10 in Harlem. It was during this period that she experienced and understood what the majority of the black population of the United States had to go through in their everyday life. Traversing the Harlem streets, living for the first time among large numbers of poor black people, seeing neglected children up close—Petry's early years in New York inevitably made impressions on her and led her to put her experiences to paper. Her daughter Liz explained to The Washington Post'' that "her way of dealing with the problem was to write this book [The Street], which maybe was something that people who had grown up in Harlem couldn’t do."