After earning her BA from St. John's College in 1977, Forrest studied Computer and Communication Sciences at the University of Michigan, where she received her MS in 1982, and in 1985 her PhD, with a thesis entitled "A study of parallelism in the classifier system and its application to classification in KL-ONE semantic networks."
After graduation Forrest worked for Teknowledge Inc. and at the Center for Nonlinear Studies of the Los Alamos National Laboratory.
In the 1990s she was also affiliated with the Santa Fe Institute, where she was Interim Vice President for the 1999–2000 term.
"[8] According to the National Academies her research since the 1990s has included "developing the first practical anomaly intrusion-detection system; designing automated responses to cyberattacks; writing an early influential paper proposing automatic software diversity and introducing instruction-set randomization as a particular implementation; developing noncryptographic privacy-enhancing data representations; agent-based modeling of large-scale computational networks; and recently, work on automated repair of security vulnerabilities.
She has conducted many computational modeling projects in biology, where her specialties are immunology and evolutionary diseases, such as Influenza and cancer.