He then studied at Harvard College, but left without taking a degree because of health problems, traveling to France, where his father had recently been appointed U.S. Consul at Saint-Étienne.

William Morton Grinnell worked for a while for the United States Consulate in Lyon.

[1] After he was admitted to the bar, Grinnell practiced law briefly in New York City.

His work there was interrupted by the outbreak of the Spanish–American War in 1898, at which time he joined the United States Army with the rank of Major.

[1] In addition to his work, Grinnell was a director of the Illinois Central Railroad, the Gunly Mountain Coal Company, the Mount Morris Bank, the Rio Grande, Sierra Madre & Pacific Railway, and the Sea Beach Land Company.