In order to understand what Homer A. Plessy stood up for, you will need to know about his family background during the time he was born. The details of the case are below this brief summary about him and his family.

Homer Adolph Plessy was born on March 17, 1862, and died on March 1, 1925. He was the son of French-speaking creoles (Haitian refugees who fled the revolution), Homer Plessy was born on St. Patrick's Day in 1862, at a time when federal troops under General Benjamin Franklin Butler were occupying Louisiana as a result of the American Civil War and had liberated Enslaved African Americans in New Orleans who had been held in bondage by enslavers, but Plessy was a Free person of color and his family came to America Free from Haiti and France. Blacks could then marry whomever they chose, sit in any streetcar seat and, briefly, attend integrated schools.
As an adult, Plessy experienced the reversal of the gains achieved under the federal occupation, following the withdrawal of federal troops in 1877 on the orders of U.S. President Rutherford B. Hayes.

Due to Plessy's phenotype being White, Plessy could have ridden in a railroad car restricted to people classified as white. However, under the racial policies of the time, he was an "octoroon" having 1/8th African-American heritage, and therefore was considered Black. Hoping to strike down segregation laws, the Citizens' Committee of New Orleans (Comité des Citoyens) recruited Plessy to deliberately violate Louisiana's 1890 separate-car law. To pose a clear test, the Citizens' Committee gave notice of Plessy's intent to the railroad, which opposed the law because it required adding more cars to its trains.

On June 7, 1892, Plessy bought a first-class ticket on a train from New Orleans and sat in the car for white riders only. The Committee had hired a private detective with arrest powers to take Plessy off the train at Press and Royal streets, to ensure that he was charged with violating the state's separate-car law and not some other misdemeanor.

Everything that the committee had organized occurred as planned, except for the decision of the Supreme Court in 1896.

By then the composition of the U.S. Supreme Court had gained a more segregationist tilt, and the committee knew it would likely lose. But it chose to press the cause anyway, [author Keith] Medley said. 'It was a matter of honor for them, that they fight this to the very end.'

Homer Plessy was born on March 17, 1862, in New Orleans to Joseph Adolphe Plessy and Rosa Debergue, members of New Orleans' French-speaking Creole society. Another in this Creole society was Plessy's compatriot, Walter L. Cohen, who obtained an appointment as customs inspector from U.S. President William McKinley.

Homer Plessy's paternal grandfather was Germain Plessy, a white Frenchman born in Bordeaux c. 1777. Germain Plessy arrived in New Orleans with thousands of other French expatriates who fled Saint-Domingue in the wake of the slave rebellion led by Toussaint L'Ouverture that wrested Haiti from Napoleon in the 1790s. Germain Plessy married Catherine Mathieu, a free woman of color, and they had eight children, including Homer Plessy's father, Joseph Adolphe Plessy

Homer Plessy's middle name would later appear as Adolphe after his father, a carpenter, on his birth certificate. Plessy belonged to Louisiana's French-speaking Creole class, which American society did not understand or accept. Plessy grew up speaking French. Adolphe Plessy died when Homer was seven years old. In 1871, his mother Rosa Debergue Plessy, a seamstress, married Victor M. Dupart, a clerk for the U.S. Post Office who supplemented his income by working as a shoemaker. Plessy too became a shoemaker. During the 1880s, he worked at Patricio Brito's shoe-making business on Dumaine Street near North Rampart. New Orleans city directories from 1886 to 1924 list his occupations as shoemaker, laborer, clerk, and insurance agent.

By 1887, Plessy had become vice-president of the Justice, Protective, Educational, and Social Club, a group dedicated to reforming public education in New Orleans. In 1888, Plessy, then twenty-five years old, was married to nineteen-year-old Louise Bordenave by Father Joseph Subileau at St. Augustine Church which is located at 1210 Gov. Nicholls Street in New Orleans. Plessy's employer Brito served as a witness. In 1889, the Plessys moved to Faubourg Tremé at 1108 North Claiborne Avenue. He registered to vote in the Sixth Ward's Third Precinct.

At age thirty, shoemaker Homer Plessy was younger than most members of the Comité des Citoyens. He did not have their stellar political histories, literary prowess, business acumen, or law degrees. Indeed, his one attribute was being white enough to gain access to the train and black enough to be arrested for doing so. This shoemaker sought to make an impact on society that was larger than simply making its shoes. When Plessy was a young boy, his stepfather was a signatory to the 1873 Unification Movement—an effort to establish principles of equality in Louisiana. As a young man, Plessy displayed a social awareness and served as vice president of an 1880s educational-reform group. And in 1892, he volunteered for a mission rife with unpredictable consequences and backlashes. Comité des Citoyens lawyers Albion Tourgee, James C. Walker and Louis Martinet vexed over legal strategy. Treasurer Paul Bonseigneur handled finances. As a contributor to The Crusader newspaper, Rodolphe Desdunes inspired with his writings. Plessy's role consisted of four tasks: get the ticket, get on the train, get arrested, and get booked.

After the Supreme Court ruling, Plessy went back into relative anonymity. He fathered children, continued to participate in the religious and social life of his community, and later sold and collected insurance premiums for the People's Life Insurance Company. He died in 1925 at the age of 62, with his obituary reading, "Homer Plessy — on Sunday, March 1, 1925, at 5:10 a.m. beloved husband of Louise Bordenave." He was buried in the Debergue-Blanco family tomb in St. Louis Cemetery #1.
Source: Wikipedia
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The Case of Plessy v. Ferguson
By: History Dot Com Editors
Updated:Jan 16, 2020 - Original:Oct 29, 2009

Plessy v. Ferguson was a landmark 1896 U.S. Supreme Court decision that upheld the constitutionality of racial segregation under the “separate but equal” doctrine. The case stemmed from an 1892 incident in which African American train passenger Homer Plessy refused to sit in a car for Blacks. Rejecting Plessy’s argument that his constitutional rights were violated, the Supreme Court ruled that a law that “implies merely a legal distinction” between whites and blacks was not unconstitutional. As a result, restrictive Jim Crow legislation and separate public accommodations based on race became commonplace.

Plessy v. Ferguson: Background and Context
After the Compromise of 1877 led to the withdrawal of federal troops from the South, Democrats consolidated control of state legislatures throughout the region, effectively marking the end of Reconstruction.

Southern Blacks saw the promise of equality under the law embodied by the 13th Amendment, 14th Amendment and 15th Amendment to the Constitution receding quickly, and a return to disenfranchisement and other disadvantages as American White supremacy reasserted itself across the South.

As historian C. Vann Woodward pointed out in a 1964 article about Plessy v. Ferguson, White and Black Southerners mixed relatively freely until the 1880s, when state legislatures passed the first laws requiring railroads to provide separate cars for “Negro” or “colored” passengers.

Florida became the first state to mandate segregated railroad cars in 1887, followed in quick succession by Mississippi, Texas, Louisiana and other states by the end of the century.

Black Resistance to Segregation
As Southern Blacks witnessed with horror the dawn of the Jim Crow era, members of the Black community in New Orleans decided to mount a resistance.

At the heart of the case that became Plessy v. Ferguson was a law passed in Louisiana in 1890 “providing for separate railway carriages for the white and colored races.” It stipulated that all passenger railways had to provide these separate cars, which should be equal in facilities.

Homer Adolph Plessy, who agreed to be the plaintiff in the case aimed at testing the law’s constitutionality, was of mixed race; he described himself as “seven-eighths Caucasian and one-eighth African blood.”

On June 7, 1892, Plessy bought a ticket on a train from New Orleans bound for Covington, Louisiana, and took a vacant seat in a whites-only car. After refusing to leave the car at the conductor’s insistence, he was arrested and jailed.

Convicted by a New Orleans court of violating the 1890 law, Plessy filed a petition against the presiding judge, Hon. John H. Ferguson, claiming that the law violated the Equal Protection Clause of the 14th Amendment.

Supreme Court Ruling in Plessy v. Ferguson
Over the next few years, segregation and Black disenfranchisement picked up pace in the South, and was more than tolerated by the North. Congress defeated a bill that would have given federal protection to elections in 1892, and nullified a number of Reconstruction laws on the books.

Then, on May 18, 1896, the Supreme Court delivered its verdict in Plessy v. Ferguson. In declaring separate-but-equal facilities constitutional on intrastate railroads, the Court ruled that the protections of 14th Amendment applied only to political and civil rights (like voting and jury service), not “social rights” (sitting in the railroad car of your choice).

In its ruling, the Court denied that segregated railroad cars for Blacks were necessarily inferior. “We consider the underlying fallacy of [Plessy’s] argument,” Justice Henry Brown wrote, “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 anything found in the act, but solely because the colored race chooses to put that construction upon it.”

John Marshall Harlan’s Dissent
Alone in the minority was Justice John Marshall Harlan, a former slaveholder from Kentucky. Harlan had opposed emancipation and civil rights for freed slaves during the Reconstruction era – but changed his position due to his outrage over the actions of white supremacist groups like the Ku Klux Klan.

Harlan argued in his dissent that segregation ran counter to the constitutional principle of equality under the law: “The arbitrary separation of citizens on the basis of race while they are on a public highway is a badge of servitude wholly inconsistent with the civil freedom and the equality before the law established by the Constitution,” he wrote. “It cannot be justified upon any legal grounds.”

Plessy v. Ferguson Significance
The Plessy v. Ferguson verdict enshrined the doctrine of “separate but equal” as a constitutional justification for segregation, ensuring the survival of the Jim Crow South for the next half-century.

Intrastate railroads were among many segregated public facilities the verdict sanctioned; others included buses, hotels, theaters, swimming pools and schools. By the time of the 1899 case Cummings v. Board of Education, even Harlan appeared to agree that segregated public schools did not violate the Constitution.

It would not be until the landmark case Brown v. Board of Education in 1954, at the dawn of the civil rights movement, that the majority of the Supreme Court would essentially concur with Harlan’s opinion in Plessy v. Ferguson..

Writing the majority opinion in that 1954 case, Chief Justice Earl Warren wrote that “the doctrine of ‘separate but equal’ has no place” in public education, calling segregated schools “inherently unequal,” and declaring that the plaintiffs in the Brown case were being “deprived of the equal protection of the laws guaranteed by the 14th Amendment.”

Sources
C. Vann Woodward, “Plessy v. Ferguson: The Birth of Jim Crow,” American Heritage(Volume 15, Issue 3: April 1964).

Landmark Cases: Plessy v. Ferguson, PBS: The Supreme Court – The First Hundred Years.

Louis Menand, “Brown v. Board of Education and the Limits of Law,” The New Yorker (February 12, 2001).

Today in History – May 18: Plessy v. Ferguson, Library of Congress.