Lawler enlisted at age 17 on September 17, 1861, as a private in Company E, 19th Illinois Volunteer Infantry and was immediately promoted to corporal.

He served with the regiment for three years and rose through the ranks, being promoted to sergeant March 1, 1863, and mustered out of the service as a 2nd lieutenant.

He is credited with being the first man of the 19th Illinois infantry over the Confederate works at the Battle of Missionary Ridge while carrying the regiment's colors.

Additionally, he sought protection for Civil War veterans who were still in the service of the U.S. Army or Navy from being unjustly dishonorably discharged.

Lawler died September 3, 1908, at his home in Rockford and is buried there in Cedar Bluff Cemetery.