An ally of African Americans since his Civil War days, later in his career Tourgée was asked to aid a committee in New Orleans that was challenging segregation on railways in Louisiana, and he was appointed the lead attorney in the landmark Plessy v. Ferguson (1896) case.

The committee was dismayed when the United States Supreme Court ruled that "separate but equal" public facilities were constitutional; this enabled segregation for decades.

Historian Mark Elliott credits Tourgée with introducing the metaphor of "color blind justice" into legal discourse.

He showed no interest in politics until the university attempted to ban the Wide Awakes, a paramilitary campaign organization affiliated with the Republican Party.

After the outbreak of the Civil War in April of the same year, Tourgée enlisted in the 27th New York Volunteer Infantry before completing his collegiate studies.

On January 21, 1863, Tourgée was captured near Murfreesboro, Tennessee and was held as a prisoner-of-war in Libby Prison in Richmond, Virginia, before his exchange on May 8, 1863.

The Tourgée couple soon moved to Greensboro, North Carolina, where he could live in a warmer climate better suited to his war injuries.

[6] He successfully advocated for equal political and civil rights for all citizens; ending property qualifications for jury duty and officeholding; requiring popular election of all state officers, including judges; founding free public education; abolishing the use of whipping posts as punishment for persons convicted of crimes; judicial reform; and uniform taxation.

During this period he confronted the increasingly violent Ku Klux Klan, which was very powerful in his district and had members who repeatedly threatened his life.

During this time, Tourgée was also appointed as one of three commissioners in charge of codifying North Carolina's previously dual law-code system into one.

The new codified civil procedures, at first strongly opposed by the state's legal practitioners, proved in time the most flexible, and informal system in the Union.

The legislatures began to pass new constitutions (beginning with Mississippi in 1890) and laws to raise barriers to voter registration to suppress the black Republican vote and to impose legal segregation in public facilities.

In September 1891 a group of prominent black leaders in New Orleans, made up of mostly men who had been free people of color before the Civil War, organized a "Citizens' Committee" to challenge this law on federal constitutional grounds.

Perhaps considered the nation's most outspoken white Radical on the "race question" in the late 1880s and 1890s, Tourgée had called for resistance to the Louisiana law in his widely read newspaper column, A Bystander's Notes.

Largely as a consequence of this column, "Judge Tourgée" had become well known in the black community for his bold denunciations of lynching, segregation, disfranchisement, white supremacy, and scientific racism.

Tourgée's first use of "color blindness" as a legal metaphor has been documented decades before, while he was serving as a Superior Court judge in North Carolina.

In his dissent in Plessy, Justice John Marshall Harlan borrowed the metaphor of "color blindness" from Tourgée's legal brief.

About 1900, Tourgée joined the Military Order of the Loyal Legion of the United States, an influential Civil War veterans' organization of Union men who had been commissioned officers.