Curtis entered the Union Army on February 13, 1862, as lieutenant colonel of the Fifty-eighth Regiment, Pennsylvania Volunteer Infantry for a period of three years. He was promoted to colonel of that regiment on May 23, 1863. Because of illness was honorably discharged as colonel on July 2.
He returned to Warren and practiced law. In 1868, he moved to Erie, Pennsylvania, and continued the practice of law. He was also interested in banking and the production of oil, and was one of the originators and builders of the Dunkirk & Venango Railroad.
Curtis was again elected as a Republican to the Forty-third Congress. He was an unsuccessful candidate for reelection in 1874. He resumed the practice of law, and died in Erie in 1883.