Born near Mount Carmel, Indiana, Cumback attended the common schools and was graduated from Miami University, Oxford, Ohio. He taught school two years. He studied law at the Cincinnati Law School. He was admitted to the bar and commenced practice in Greensburg, Indiana, in 1853.
Cumback was elected as an Opposition Party candidate to the Thirty-fourth Congress (March 4, 1855–March 3, 1857). He was an unsuccessful candidate for reelection in 1856. He resumed the practice of law. He was appointed a paymaster in the Army and served throughout the Civil War. He served as member of the State senate in 1866. The 16th Lieutenant Governor of Indiana in 1868. He was an unsuccessful candidate for election to the United States Senate in 1869. President Grant nominated Cumback as the U.S. Minister to Portugal in 1870 but he declined the appointment. United States revenue collector 1871-1883. Trustee of DePauw University, Greencastle, Indiana. He was an unsuccessful candidate for nomination for Governor in 1896. He died in Greensburg, Indiana, July 31, 1905. He was interred in South Park Cemetery.
This article incorporates public domain material from websites or documents of the Biographical Directory of the United States Congress.