His research interests include: atmospheric and oceanic waves and turbulence, geophysical fluid dynamics, physics of the planetary interior, and planetary climate.
He is notable for his seminal contributions to the understanding of the dynamics of the deep Earth, both concerning the nature of the mantle convection process and the circulation of the visco-elastic interior caused by the loading of the surface by continental scale ice sheet loads. His gravitationally self-consistent global theory of Ice-Earth-Ocean interactions has become widely employed internationally in the explanation of the changes of sea level that accompany both the growth and decay of grounded ice on the continents, both during the Late Quaternary era of Earth history and under modern global warming conditions. His models of the space-time variations of continental ice cover since the last maximum of glaciation are employed universally to provide the boundary conditions needed to enable modern coupled climate models to be employed to reconstruct past climate conditions. A most notable contribution to work of this kind has been his theory of the so-called Dansgaard-Oeschger millennial timescale oscillation of glacial climate. He has been the primary contributor to the global reconstructions ICE-3G, ICE-4G, ICE-5G (VM2), and the most recent ICE-6G (VM5)model. These models are important for the quantification of post-glacial rebound and late Pleistocene to Holocene variations in sea level.
^Tushingham, A. M.; Peltier, W. R. (1991). "Ice-3G: A New Global Model of Late Pleistocene Deglaciation Based Upon Geophysical Predictions of Post-Glacial Relative Sea Level Change". Journal of Geophysical Research. 96 (B3): 4497–4523. Bibcode:1991JGR....96.4497T. doi:10.1029/90JB01583.
^Peltier, W. R. (1994). "Ice Age Paleotopography". Science. 265 (5169): 195–201. Bibcode:1994Sci...265..195P. doi:10.1126/science.265.5169.195. PMID17750657. S2CID 29508590.
^Peltier, W.R. (2004). "Global glacial isostasy and the surface of the ice-age Earth: the ICE-5G (VM2) Model and GRACE". Annual Review of Earth and Planetary Sciences. 32: 111–149. Bibcode:2004AREPS..32..111P. doi:10.1146/annurev.earth.32.082503.144359.