He received his PhD from Harvard in 1963 with a dissertation on The Post-Classic Period in the Southern Maya Lowlands.
In the late 1980s, Cowgill co-directed excavations at the Feathered Serpent Pyramid at Teotihuacán with Saburo Sugiyama and Rubén Cabrera.
Several of Cowgill's published articles on Teotihuacán are among the most important syntheses of archaeological information on this ancient city.
He and his students produced innovative studies of the spatial organization of Teotihuacán as determined from his artifact database.
Cowgill made a number of major contributions to the comparative study of ancient states and cities.