Patsy O'Connell joined 3M (Minnesota Mining and Manufacturing Company) as a laboratory technician. At the time, career options for women in science were limited, but 3M offered a path for advancement.

While working with a fluoro-chemical rubber intended for use in jet fuel hoses, Patsy and her colleague Samuel Smith accidentally spilled some of the substance on a canvas shoe. They tried to clean it off but found that the treated area resisted oil, water, and other liquids, leading to the discovery of Scotchgard's stain-repellent properties.

Following the accidental discovery, Patsy and Samuel Smith dedicated their efforts to refining and developing the fluorochemical polymer into a commercially viable product. This involved extensive testing, experimentation, and collaboration with other 3M scientists.

Patsy O'Connell Sherman and Samuel Smith filed for a patent for Scotchgard, officially recognizing their invention and its unique stain-repellent properties. This marked a significant milestone in their careers and the development of the product.

Patsy continued to work at 3M, contributing to further research and development efforts related to fluorochemicals and other materials. She held various technical and managerial positions within the company.

Patsy O'Connell Sherman retired from 3M after a distinguished career spanning four decades. Her contributions to the company, particularly the invention of Scotchgard, left a lasting legacy.