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. She went to college and graduated with a Ph.G. degree from 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, which brought her to New York. She not only wrote articles for newspapers such as The Amsterdam News, or The People's Voice, and published short stories in The Crisis, but 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, which maybe was something that people who had grown up in Harlem couldn’t do.”
Petry's most popular novel The Street was published in 1946 and won the Houghton Mifflin Literary Fellowship with book sales topping a million copies.
Back in Old Saybrook in 1947, Petry worked on Country Place (1947), The Narrows (1953), other stories, and books for children, but they have never achieved the same success as her first book. She drew on her personal experiences of the hurricane in Old Saybrook in Country Place. Although the novel is set in the immediate aftermath of World War II, Petry identified the 1938 New England hurricane as the source for the storm that is at the center of her narrative.
Petry remained in Old Saybrook for the rest of her life. She died at the age of 88 on April 28, 1997. She was outlived by her husband George, who died in 2000, and her only daughter, Liz Petry.