After the war he returned to Fields Store and worked as a cotton weigher and justice of the peace while he studied law. After admission to the bar in 1875, Pinckney moved to the county seat, Hempstead, where he was district attorney for the Twenty-third Judicial District of Texas from 1890 until 1900. From 1900 to 1903 he served as Waller county judge. He won election to the United States House of Representatives as a Democrat in 1903 and filled a seat vacated by Thomas H. Ball. Pinckney represented the First Congressional District of Texas in the Fifty-eighth and Fifty-ninth congresses. He was a prohibitionist.
On April 24, 1905, he died from gunshot wounds received while attempting to stop a fight at the Waller County Courthouse, where he and members of the Prohibition League were considering a petition calling for the Texas Rangers to enforce a recently enacted prohibition law. Pinckney, who was unarmed, his brother Thomas D., and two other men died. His accused murderer, Roland Brown, was acquitted. Pinckney, a bachelor, was survived by his sister, Susanna S. Pinckney, and a brother, Robert Pinckney. After a funeral conducted by a Baptist minister and members of the Masonic lodge, Pinckney was buried in the Hempstead City Cemetery. As a result of the publicity surrounding his death, the town of Hempstead became known as "Six-Shooter Junction."
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