After graduating from Ohio University in 1950, Grasselli Brown was offered a job position at Standard Oil (now BP America) in Cleveland as a project leader. From 1950 to 1978, she worked closely with an instrument called an infrared spectrometer. This device is used to measure the absorbance, emission, and reflection of infrared light interacting with a molecule and also measures the vibrations of atoms to identify functional groups.
During her time at Standard Oil, Grasselli Brown used the infrared spectrometer to examine the concentration of materials, and sought to find industrial applications for it. 
As a project leader, she analyzed the formulations of World War II German airplane fuels to understand how the German planes were able to extend their flight ranges. She also consulted with the coroner's office in Cleveland to analyze unknown samples at crime scenes.
In 1978, she became the manager of the analytical science laboratory, working there until 1983. In 1983, she became the director of the technological support department, working there until 1985, when she became the first female director of corporate research from 1985 to 1988. Grasselli Brown retired in January 1989 as the company's highest ranking female employee.