Giesy was credited with being the first scientist to discover toxic per- and poly-fluoroalkyl [PFAS] chemicals in the environment.

His discoveries also include the photo-enhanced toxicity and the presence of perfluorinated chemicals in the environment.

John P. Giesy interconnects Toxicology and Biochemistry in the investigation of issues within Toxicity. The study incorporates disciplines such as Bay, Hydrology, Water pollution, Dry weight and Pollution in addition to Sediment.

The concepts of his Bioassay study are interwoven with issues in Aryl hydrocarbon receptor and In vitro, Potency.

His primary areas of study are Environmental chemistry, Sediment, Ecology, Toxicity and Water quality. His Environmental chemistry research is multidisciplinary, incorporating elements of Environmental engineering, Pollutant, Contamination, Phosphorus and Bioassay. Many of his studies on Bioassay apply to Aryl hydrocarbon receptor as well.

As part of his studies on Sediment, John P. Giesy often connects relevant areas like Pollution.

His study in Eutrophication, Zooplankton, Benthic zone and Invertebrate falls within the category of Ecology. In his research on the topic of Water quality, Ecosystem is strongly related with Aquatic ecosystem.

He was elected as member of the Euorpean Academy of Engineering in 2008.