1815–86, American jurist, associate justice of the U.S. Supreme Court (1862–77), b. Cecil co., Md., grad. Kenyon College, 1832; cousin of Henry Winter Davis. In 1836 he settled as a lawyer in Bloomington, Ill., his home thereafter. From 1848 to 1862 Davis presided over the eighth judicial circuit in Illinois, famous because Abraham Lincoln practiced in its courts. An intimate of Lincoln (the tall, spare Lincoln and the corpulent Davis often bunked together in traveling the circuit), he successfully managed his friend's campaign to secure the Republican nomination for the presidency at Chicago in 1860. Davis and Leonard Swett, another lawyer from the eighth circuit active in Lincoln's cause, gave several political assurances without Lincoln's knowledge (notably one to Simon Cameron of Pennsylvania), which Lincoln reluctantly honored. Lincoln appointed (1862) Davis to the U.S. Supreme Court. Not especially learned in the law, he nevertheless wrote one of the most important opinions in the history of the court in Ex parte Milligan (1866). The decision, denouncing arbitrary military power, became famous as one of the bulwarks of civil liberty in the United States. Davis, who did not allow his judicial position to interfere with his political ambitions, was nominated for President by the Labor Reform Convention at Columbus, Ohio, in 1872, but withdrew when he failed to win the nomination of the Liberal Republican party as well. In 1877 he resigned from the court to serve (1877–83) as U.S. Senator from Illinois.
- See biography by W. L. King (1960).