Horace Gray (March 24, 1828 – September 15, 1902) was an American jurist who ultimately served on the United States Supreme Court. He was an active in public service and a great philanthropist to the City of Boston. Notably, he founded the Boston Public Garden in 1837.

Gray was born in Boston, Massachusetts, to the prominent Boston Brahmin merchant family of William Gray. He enrolled at Harvard College at the age of 13, graduated four years later and traveled in Europe for a time before returning home following a series of business problems for his family. He studied law at Harvard, although he did not receive a degree. Gray entered the bar in 1851.

In 1854, he was named Reporter of Decisions for the Massachusetts Supreme Judicial Court, a very prestigious appointment for so young a man and one which allowed him to edit numerous volumes of court records and provided for some independent legal writing, all of which earned him a very good reputation as a scholar and legal historian. This reputation made him a natural choice when a vacancy opened up on the Supreme Judicial Court in 1864. At age 36, Gray was youngest appointee in that court's history.

Gray maintained a good reputation on the state supreme court, and became the court's Chief Justice in 1873. While serving as chief justice, Gray hired Louis D. Brandeis as a clerk, becoming the first justice of that court to hire a clerk.

In 1881, President Chester A. Arthur nominated Gray to a vacancy on the Supreme Court of the United States; he was confirmed the following day. In 1889, Gray married Jane Matthews, who was the widow of his former colleague on the court, Thomas Stanley Matthews. As he had been in Massachusetts, Gray was the first Justice of the U.S. Supreme Court to hire a law clerk. He used his own funds to pay the clerk's salary, as no government money was appropriated for this purpose at the time. Gray served on the U.S. Supreme Court for 24 years, resigning in July, 1902, gravely ill. He was succeeded by a fellow Massachusetts native, Oliver Wendell Holmes, Jr., who coincidentally had succeeded Gray on the Massachusetts Supreme Judicial Court.

Gray was one of the few Supreme Court appointees in the latter half of the 1800s who had not previously been a politician, and he maintained the opinion that law and politics were entirely separate fields. His opinions, both concurring and dissenting, were generally very long and weighted with legal history.

Gray is best known for his decision in Pollock v. Farmers' Loan & Trust Co. This case was heard twice, though only the second hearing resulted in a decision; the justices wished to rehear the case feeling that the opinions written had not adequately explained their view of the situation (the case was about the constitutionality of a national income tax). After the first hearing, Gray wrote that he sided with the defendant (Farmer's Loan & Trust), arguing that the tax was indeed constitutional. He was in the minority, however. After the second hearing, Gray changed his stance, joining with the majority in favor of the plaintiff. He chose not to write a dissenting or concurring opinion, in either hearing.

Horace Gray was also the author of the 1898 case United States v. Wong Kim Ark, ruling that a child born in United States to foreign parents is automatically a citizen of the United States.

Gray was the half-brother of John Chipman Gray, a lawyer and long-time professor at Harvard Law School.

*Data drawn in part from the Supreme Court Historical Society and Oyez.