Ward's academic career has included teaching posts and professional connections with Ohio State University, the NASA Astrobiology Institute, the University of Calgary, McMaster University, and the California Institute of Technology. He was elected as a Fellow of the California Academy of Sciences in 1984.

Peter Ward specializes in the Cretaceous—Tertiary extinction event and mass extinctions generally. He has published books on biodiversity and the fossil record. His 1992 book On Methuselah's Trail received a "Golden Trilobite Award" from the Paleontological Society as the best popular science book of the year. Ward also serves as an adjunct professor of zoology and astronomy.

Ward is co-author, along with astronomer Donald Brownlee, of the best-selling Why Complex Life Is Uncommon in the Universe, published in 2000. In that work, the authors suggest that the universe is fundamentally hostile to advanced life, and that, while simple life might be abundant, the likelihood of widespread lifeforms as advanced as those on Earth is marginal.

According to Ward's April 2007 book, Under a Green Sky, all but one of the major extinction events in history have been brought on by climate change ... the same global warming that occurs today. The author argues that events in the past can give valuable information about the future of our planet. Reviewer Doug Brown goes further, stating "this is how the world ends". Scientists at the Universities of York and Leeds also warn that the fossil record supports evidence of impending mass extinction.

The Medea Hypothesis is a term coined by Ward for the anti-Gaian hypothesis that multicellular life, understood as a superorganism, is suicidal.

Peter Ward was featured in the PBS's Evolution Series to discuss the evidence for evolution in the geologic record and has appeared on NOVA scienceNOW.