[2][3] The decision legitimized the many state "Jim Crow laws" re-establishing racial segregation that had been passed in the American South after the end of the Reconstruction era in 1877.

Justice John Marshall Harlan was the lone dissenter from the Court's decision, writing that the U.S. Constitution "is color-blind, and neither knows nor tolerates classes among citizens", and so the laws distinguishing races should have been found unconstitutional.

[6] However, beginning in 1954 with Brown v. Board of Education, which held that the "separate but equal" doctrine is unconstitutional in the context of public schools, a series of the Court's later decisions have severely weakened Plessy to the point that it is considered to have been de facto overruled.

[9] The Comité eventually persuaded Homer Plessy, a man of mixed race who was an "octoroon" (person of seven-eighths white and one-eighth black ancestry), to participate in an orchestrated test case to challenge the Act.

[12] Additionally, the Comité des Citoyens hired a private detective with arrest powers to detain Plessy, to ensure that he would be charged for violating the Separate Car Act, as opposed to vagrancy or some other offense.

However, the judge presiding over his case, John Howard Ferguson, ruled that Louisiana had the right to regulate railroad companies while they operated within state boundaries.

The Court first dismissed any claim that the Louisiana law violated the Thirteenth Amendment, which, in the majority's opinion, did no more than ensure that black Americans had the basic level of legal equality needed to abolish slavery.

The Court said that although the Fourteenth Amendment was meant to guarantee the legal equality of all races in the United States, it was not intended to prevent social or other types of discrimination.

[26] Plessy's lawyers had argued that segregation laws inherently implied that black people were inferior, and therefore stigmatized them with a second-class status that violated the Equal Protection Clause.

If this be so, it is not by reason of anything found in the act, but solely because the colored race chooses to put that construction on it.The Court rejected the notion that the law marked black Americans with "a badge of inferiority", and said that racial prejudice could not be overcome by legislation.

Harlan strongly disagreed with the Court's conclusion that the Louisiana railcar law did not imply that black people were inferior, and he accused the majority of being willfully ignorant on the issue.

The thing to accomplish was, under the guise of giving equal accommodation for whites and blacks, to compel the latter to keep to themselves while traveling in railroad passenger coaches.

No one would be so wanting in candor as to assert the contrary.To support his argument, Harlan pointed out that the Louisiana law contained an exception for "nurses attending children of the other race".

[32] In a now-famous passage, Harlan forcefully argued that even though many white Americans of the late 19th century considered themselves superior to those of other races, the U.S. Constitution was "color-blind" regarding the law and civil rights.

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 predicted the Court's decision would eventually become as infamous as its 1857 decision Dred Scott v. Sandford, in which the Court had ruled that black Americans could not be citizens under the U.S. Constitution and that its legal protections and privileges could never apply to them.

[41][page needed] The prospect of greater state influence in matters of race worried numerous advocates of civil equality, including Supreme Court Justice John Harlan, who wrote in his Plessy dissent, "we shall enter upon an era of constitutional law, when the rights of freedom and American citizenship cannot receive from the nation that efficient protection which heretofore was unhesitatingly accorded to slavery and the rights of the master.

"[39] Harlan's concerns about the encroachment on the 14th Amendment would prove well-founded; states proceeded to institute segregation-based laws that became known as the Jim Crow system.

[42] In addition, from 1890 to 1908, Southern states passed new or amended constitutions including provisions that effectively disenfranchised blacks and thousands of poor whites.

[45] Both point to a passage of Harlan's Plessy dissent as particularly troubling:[46][47] 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.

[48]New Orleans historian Keith Weldon Medley, author of We As Freemen: Plessy v. Ferguson, The Fight Against Legal Segregation, said the words in Justice Harlan's "Great Dissent" were taken from papers filed with the court by "The Citizen's Committee".

[50]: 16–18  The principles of Plessy v. Ferguson were affirmed in Lum v. Rice (1927), which upheld the right of a Mississippi public school for white children to exclude a Chinese American girl.

[51] Jim Crow laws and practices spread northward in response to a second wave of African-American migration from the South to northern and midwestern cities.

Some established de jure segregated educational facilities, separate public institutions such as hotels and restaurants, separate beaches among other public facilities, and restrictions on interracial marriage, but in other cases segregation in the North was related to unstated practices and operated on a de facto basis, although not by law, among numerous other facets of daily life.

Historian Rogers Smith noted on the subject that "lawmakers frequently admitted, indeed boasted, that such measures as complex registration rules, literacy and property tests, poll taxes, white primaries, and grandfather clauses were designed to produce an electorate confined to a white race that declared itself supreme", notably rejecting the 14th and 15th Amendments to the American Constitution.