Born in Jessamine County, Kentucky, Shanklin attended a private school at Nicholasville, Kentucky. He studied law. He was admitted to the bar and commenced practice in Nicholasville. He served as member of the State house of representatives in 1838 and 1844. He was appointed Commonwealth attorney in 1854. He was again a member of the State house of representatives, and served from 1861 to 1865.
Shanklin was elected as a Democrat to the Thirty-ninth Congress (March 4, 1865 – March 3, 1867). He retired to his farm in Jessamine County, where he died April 1, 1883. He was interred at Lexington Cemetery.