Davis, a cousin of Henry Winter Davis, was born to a wealthy family in Cecil County, Maryland, where he attended the public schools. After graduating from Kenyon College in Gambier, Ohio, in 1832 he went on to study law at Yale University, and upon his graduation from Yale in 1835, moved to Bloomington, Illinois, to practice law. From 1848-1862, Davis presided over the local judicial circuit, the same circuit where attorney Abraham Lincoln was practicing. Davis assisted Lincoln in Lincoln's presidential campaign in 1860.
In 1862, President Lincoln appointed Davis to the U.S. Supreme Court, where he became famous for writing one of the most profound decisions in the Supreme Court history, Ex Parte Milligan (1866). In that decision, the court set aside the death sentence imposed during the Civil War by a military commission upon a civilian, Lambdin P. Milligan. Milligan had been found guilty of inciting insurrection. The Supreme Court held that since the civil courts were operative, the trial of a civilian by a military tribunal was unconstitutional. The opinion denouced arbitrary military power, effectively becoming one of the bulwarks of held notions of American civil liberty.
After refusing calls to become Chief Justice of the Supreme Court, Davis, a registered independent, was nominated for President by the Labor Reform Convention in 1872, but withdrew when he failed to receive the Liberal Republican Party nomination. He resigned from the Supreme Court in 1877 to serve as a U.S. Senator from Illinois until 1883.
Lincoln was a deft politician, emerging as a wartime leader who was skilled at balancing competing considerations, and adept at getting rival groups to work together toward a common goal.
His leadership qualities were evident in his handling of the border slave states at the beginning of the fighting, in his defeat of a congressional attempt to reorganize his cabinet in 1862, and his defusing of the peace issue in the 1864 presidential campaign.
There was more than a year and a half of trial to suppress the rebellion before the proclamation issued, the last one hundred days of which passed under an explicit notice that it was coming, unless averted by those in revolt, returning to their allegiance.
Davis was born in Millicent, South Australia, but went to school in Melbourne.
Davis had become involved with the Liberal Party during the early 1990s, serving as a delegate on several party committees, and acting as a delegate to the party's State Council between 1993 and 1995.
Davis is a factional powerbroker in the Liberal Party, and was the source of numerous tensions during the reign of Robert Doyle as a notable opponent of his leadership.