Professor Guillermo Gallego joined Columbia University's Industrial Engineering and Operations Research Department in 1988 where he has been conducting research in the areas of inventory theory, supply chain management, revenue management, and dynamic pricing. He was named an Informs Fellow in 2012 and has been the recipient of many awards including the Informs Revenue Management Section Prize (2005), the Revenue Management Historical Prize (2011) and the Revenue Management Practice Prize (2012). Professor Gallego has published influential papers in the leading journals of his field where he has also occupied a variety of editorial positions. His work has been supported by numerous industrial and government grants.

Professor Gallego has consulted for Hewlett Packard, IBM, Lucent, Nomis Solutions, and Sabre Airline Solutions. He has also worked with government agencies such as the National Research Council, the National Science Foundation and the Ireland Development Agency. His graduate students are associated with prestigious universities. He spent his 1996–97 sabbatical at Stanford University and was a visiting scientist at the IBM Watson Research Center from 1999 to 2003. He was the chairman of the IEOR Department from July 2002 to June 2008.