McNamara earned her doctoral degree in Infectious Diseases and Microbiology at University of Pittsburgh School of Public Health.

After graduating, she joined the Centers for Disease Control and Prevention as a postdoctoral resident in Public Health and Medical Microbiology.

[citation needed] McNamara was a Senior Staff Microbiologist at the National Institutes of Health Clinical Center for two years before moving to the United States Department of Agriculture as Director of Microbiology in 1992.

At the time she joined the Food Safety and Inspection Service the majority of focus was on chemical adulterants.

[8] She established a food safety research fund at Georgetown University, and developed a program for Listeria control and environmental monitoring.