He then moved to New York in 1860 to continue the study of law, but returned to Wisconsin when the Civil War began.

At the Battle of Nashville, Weissert was wounded by a musket ball in the leg just above the knee.

He was subsequently offered an appointment to the United States Military Academy, but he declined due to his wound.

Weissert joined the Grand Army of the Republic in 1866[1] and served as commander of E. B. Wilcott Post #1 in Milwaukee.

President Theodore Roosevelt appointed Weissert to the Board of Visitors of the U.S. Military Academy in 1904.