On June 7, 1892, a racially mixed shoemaker from New Orleans named Homer Plessy bought a first-class ticket for a train bound for Covington, La., and took a seat in the whites-only car. He was asked to leave, and after he refused, he was dragged from the train and charged with violating the Louisiana Separate Car Act. He pleaded guilty and was fined $25.

On Friday, nearly 130 years after the arrest, the Louisiana Board of Pardons voted to clear his record.

“There is no doubt that he was guilty of that act on that date,” Jason Williams, the Orleans Parish district attorney, told the board during a brief hearing on Friday. “But there is equally no doubt that such an act should have never been a crime in this country.”

The arrest elevated Plessy into the central figure in a legal battle that reached the U.S. Supreme Court. The landmark ruling that resulted in the case, Plessy v. Ferguson, came to be regarded as one of most shameful decisions in the court’s history as well as one of the most consequential. It endorsed the “separate but equal” doctrine and gave legal backing to the Jim Crow laws that segregated and disenfranchised African Americans in the South for decades.

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In making their decision, board officials cited the Avery C. Alexander Act, legislation named for the civil rights leader and longtime member of the Louisiana House of Representatives, which calls for pardoning individuals who had been convicted of violating laws enacted with the purpose of enforcing segregation or discrimination.

The 1890 Louisiana Separate Car Act was precisely that kind of law, part of a flurry of segregationist legislation pursued across the South in an effort to construct a new racist order after Reconstruction.

“It has never been used,” Mr. Williams said of the Alexander Act. “It almost makes you think it was designed for just this moment, for Homer Plessy.”

Plessy had boarded the East Louisiana Railway’s No. 8 train in New Orleans intending to get arrested. He was an activist who was part of a local civil rights group that was infuriated by the Separate Car Act. The group chose Plessy as the one to ride the train because he could pass for a white man.