As an undergraduate at Harvard University, Fiore worked on ozone smog for her honors thesis. As a graduate student at Harvard, Fiore worked with the Harvard Atmospheric Chemistry Modeling Group. Before becoming a professor, Fiore continued her research at the Atmospheric and Ocean Sciences Program at Princeton University, the Geophysical Fluid Dynamics Laboratory, and the National Center for Atmospheric Research. In 2011, Fiore started as a professor in the Department of Earth and Environmental Sciences and Lamont–Doherty Earth Observatory of Columbia University in Palisades, NY. She became a full professor in 2016. In her time at Columbia, she taught a variety of classes, including Introduction to Atmospheric Chemistry, Insights into Climate and Carbon Cycling from Simple Models, Dust in the Earth System, and Atmosphere Tutorial: Chemistry. In 2021 Fiore moved to Massachusetts Institute of Technology when she was named the first Peter H. Stone and Paola Malanotte Stone Professor in Earth, Atmospheric and Planetary Sciences.
Her fields of interest are air quality, climate change and variability, and atmospheric chemistry. She studies connections between the biosphere and the atmosphere, changes and patterns in atmospheric composition, and the relationship between climate and chemistry.
In addition to being a professor and researcher, Fiore participates in a numerous of professional activities. Since 2016 she has been the Principal Investigator with the NASA Health and Air Quality Applied Sciences Team. She has also been a member of the Board on Atmospheric Sciences and Climate of the National Academy of Sciences, the American Meteorological Society Statement on Atmospheric Ozone, the Steering Committee for NYSERDA-sponsored NESCAUM Workshop on New York City Metropolitan Area Energy and Air Quality Data Gaps, and the Steering Committee's IGAC/SPARC Chemistry-Climate Modeling Initiative since 2014, 2017, 2017, and 2013 respectively.