During the Civil War, he commanded the 3rd Wisconsin Infantry Regiment and received an honorary brevet to the rank of brigadier general.

[4] Hawley originally served in the United States Army during the Mexican–American War,[4] where he achieved the rank of sergeant.

After the outbreak of the American Civil War, Hawley was commissioned an officer in the Union Army and helped to organized the 3rd Wisconsin Infantry Regiment.

[2] On January 13, 1866, President Andrew Johnson nominated Hawley for appointment to the grade of brevet brigadier general of volunteers to rank from March 16, 1865,[4] for gallant services in the campaigns in Georgia and South Carolina, and the United States Senate confirmed the appointment on March 12, 1866.

[2] In May 1866, he re-joined the U.S. Army as a second lieutenant in the 11th U.S. Infantry Regiment[2] and was stationed in Virginia that year.