[7][8] In 1984,[7] Delworth joined the Climate Dynamics Group of the Geophysical Fluid Dynamics Laboratory (GFDL), part of the Office of Oceanic & Atmospheric Research of the National Oceanic & Atmospheric Administration (NOAA) of the U.S. Department of Commerce, in Princeton, NJ.

In addition Delworth has been a lecturer in atmospheric and oceanic sciences at Princeton University since 2008.

[7][9] Delworth has collaborated with many others including 2021 Nobel Laureate Syukuro Manabe, who created the first climate models to show the effects of carbon dioxide building up in the atmosphere, Ronald J. Stouffer, Michael E. Mann, and Rong Zhang.

[10][11][12][13] Delworth serves on the Syukuro Manabe Climate Research Award Committee of the American Meteorological Society.

"[2][20] He has collaborated widely on studies of the role of the ocean in extreme weather such as warming temperatures, drought, tropical cyclones, flooding and winter storms.