Harlan was innate into the large Kentucky slaveholding family, his father the easily-known Kentucky politician & previous Congresswoman. Harlan graduated from either Centre College and began his career when he joined his father's law practice inside 1852. He was the Whig like his father, but once a person dissolved he began switching between many parties, like a Know Nothings. Harlan was elective county judge of Franklin County, Kentucky in 1858. He enlisted in the Union Army in 1861 when the Civil War broke out, rising to the rank of colonel.

Harlan firmly supported slavery however fought to preserve a Union. He said he would resign in case President Lincoln signed the Emancipation Proclamation. He did non resign whilst Lincoln did sign it, however did leave a army two or three months late to care for his personal as punishment a demise of his father.

He resumed his career & was elective Kentucky Attorney General in 1863. Harlan joined a Republican party in 1868 & remained a Republican for a rest of his life, and, befitting his fresh person, he turned strongly against slavery, calling it "the most perfect despotism that ever existed on this earth." He run governor inside 1871 and 1875, losing both days. He was appointed to the Supreme Court within 1877 by President Rutherford B. Hayes, whom he had helped win the 1876 Republican party presidential nomination.

On a Court, Harlan became called "the great dissenter." When a Court moved out of interpreting a Reconstruction Amendments to protect African Americans, Harlan wrote many silver dissents within trend lines of equal rights for African Americans & racial equality. In the Civil Rights Cases (1883), a Supreme Court struck down the Civil Rights Work of 1875, holding that the work exceeded Congressional powers. Harlan alone dissented smartly, charging that a majority got subverted a Reconstruction Amendments: "The substance and spirit of the recent amendments of the constitution have been sacrificed by a subtle and ingenious verbal criticism."

Around 1896, a Supreme Court handed down one of a virtually all reviled decisions within its history, Plessy v. Ferguson (1896), which established the doctrine of "separate but equal" as it legitimized Southern segregation practices. A Court, speaking across Justice Henry B. Brown, held that separation of the races was not inherently unequal, and any inferiority felt by blacks at having to use separate facilities was an illusion: "We consider the underlying fallacy of the plaintiff's argument to consist in the assumption that the enforced separation of the two races stamps the colored race with a badge of inferiority. If this be so, it is not by reason of any-thing found in the act, but solely because the colored race chooses to put that construction upon it." (When a Court held that separate facilities experienced to exist as compeer, around practice a facilities intended for blacks were inevitably subpar.) Harlan was againside alone in dissenting. Within stirring language that would inspire Civil Rights militant for generations supplementary, Harlan declared: "But in view of the constitution, in the eye of the law, there is in this country no superior, dominant, ruling class of citizens. There is no caste here. Our constitution is color-blind, and neither knows nor tolerates classes among citizens. In respect of civil rights, all citizens are equal before the law. The humblest is the peer of the most powerful. The law regards man as man, and takes no account of his surroundings or of his color when his civil rights as guaranteed by the supreme law of the land are involved." Harlan argued that the Louisiana law under consideratiin in the experience, which forced separation of white & nigrify rider on car, was a "badge of servitude" that degraded African-Americans, & aright predicted that a Court's opinion would be when ill-famed when its opinion in the Dred Scott case.

Harlan's liberal views in race did non reach the Chinese. He wrote this coloured statement inside his dissent: "There is a race so different from our own that we do not permit those belonging to it to become citizens of the United States. Persons belonging to it are, with few exceptions, absolutely excluded from our country. I allude to the Chinese race. But by the statute in question, a Chinaman can ride in the same passenger coach with white citizens of the United States, while citizens of the black race in Louisiana, many of whom, perhaps, risked their lives for the preservation of the Union, who are entitled, by law, to participate in the political control of the State and nation, who are not excluded, by law or by reason of their race, from public stations of any kind, and who have all the legal rights that belong to white citizens, are yet declared to be criminals, liable to imprisonment, if they ride in a public coach occupied by citizens of the white race."

Harlan was a 1st justice to argue that a Fourteenth Amendment incorporated a Bill of Rights against the states, within Hurtado v. California (1884). His argument would late become adopted by Hugo Black, and now these are widely accepted that a Fourteenth Amendment incorporates 100% of the Bill of Rights.

Harlan likewise dissented in Lochner v. New York, though he agreed with the majority "that there is a liberty of contract which cannot be violated even under the sanction of direct legislative enactment."

Harlan died in October 14, 1911 after 34 years with a Supreme Court, one of a hanker tenures around history. Numerous regard Harlan when one of a first, controversial, & windy Supreme Court Justices within U.S. History.