After receiving his Ph.D. in Geology in 1966, Greeley worked for Standard Oil Company of California. Through military duty, he was assigned to NASA's Ames Research Center in 1967 where he worked in a civilian capacity in preparation for the Apollo missions to the Moon. Subsequently, he remained at NASA to conduct research in planetary geology. With the results from planetary missions in the early 1970s, attention shifted to Mars and research on volcanism and aeolian processes through the analysis of Mariner 6, 7, and 9 data. Results from this work were applied as a science team member on the Mars Viking Mission, 1976-80.
In 1977, Greeley joined the faculty at Arizona State University with a joint professorship in Geology and the Center for Meteorite Studies. Current projects include study of wind processes on Earth, Mars, and Venus, field studies of basaltic volcanism, and photogeological mapping of planets and satellites. Planetary mission involvement includes science team membership on the Galileo Jupiter mission, Mars Exploration Rovers, and the European Space Agency Mars Express mission. Greeley has served on various NASA and National Academy of Science panels to assess space science and planetary geology activities. He has chaired the NASA Planetary Cartography Working Group, the National Academy of Sciences Committee on Lunar and Planetary Exploration, and the NASA Mars Exploration Program Analysis Group; he currently chairs the NASA Astobiology Institute Europa Focus Group. He is author or co-author of 14 books and more than 240 papers.