John Robert Cravens was born in Madison, Indiana on November 22, 1819, to Robert Cravens and Sarah Grover Paul Cravens. He graduated from Indiana University with an A.B. in 1840 and an A.M. degree at an unknown date. After graduation, Cravens read law in Madison in the office of Joseph G. Marshall. Cravens was involved in milling with W.W. Page Sr. for several years until their investments burned to the ground. He was then elected president of the Madison and Indianapolis Railway Company and the Shelbyville and Columbus railway. Cravens remained in the office until the companies were reorganized, and he voluntarily retired. He then served for a short time as an editor and proprietor of the "Madison Banner", a Whig newspaper.

Cravens was active in Indiana politics. Cravens served in the Indiana State Senate from 1854 to 1862 and 1866 to 1870. He was the Presiding Officer, Senate President Pro Tempore from 1860 to 1862 in the Indiana Senate. Cravens served as Acting Lieutenant Governor of Indiana from 1861 to 1863. He served in other roles including as a judge in the Jefferson Circuit Court and as a school trustee in Madison. Cravens was also involved with the Madison Opera House Company, the Madison Hotel, and the Madison Foundry.

Cravens married Drusilla Lanier on February 1, 1844. They had 12 children with 11 living to adulthood. Their children were John, Robert, James, Alexander, William, Elizabeth, Joseph, Mary, Drusilla, Margaret (died in infancy), and Franklin. Cravens died on March 26, 1899 at his home, Fairmount, in Madison, Indiana.