Born in Philadelphia, Pennsylvania, the son of Irish Catholic immigrants, he attended St. Joseph's College and the Collegiate Institute at Benicia, California. After being admitted to the California bar in 1865, he became District Attorney for Solano County and then campaigned for and won a seat in the California State Assembly for two years. He retired after one term and an unsuccessful bid for Speaker. After two unsuccessful attempts, McKenna was elected to the United States House of Representatives in 1885 and served for four terms. He was appointed to the Ninth Circuit Court of Appeals in 1892 by President Benjamin Harrison. In 1897 he was appointed the 42nd Attorney General of the United States by President William McKinley, and served in that capacity until 1898. He was then appointed an Associate Justice of the Supreme Court of the United States to succeed Justice Stephen J. Field. McKenna was named by President McKinley on January 28, 1898 and took his seat the next day. Conscious of his limited credentials, McKenna took courses at Columbia Law School for several months to improve his legal education before taking his seat on the Court. Although he never developed a consistent legal philosophy, McKenna was the author of a number of important decisions. One of the most notable was his opinion in the case of United States v. U.S. Steel Corporation which held that antitrust cases would be decided on the "rule of reason" principle—only alleged monopolistic combinations that are in unreasonable restraint of trade—are illegal. McKenna was known to be a centrist, and was one of the most vigorous members of the Supreme Court. He authored 614 majority opinions, and 146 dissenting opinions during his time on the bench. His passionate rebuttal to the denial of "pecuniary benefit" to a wife whose husband had been killed while working on the railroad was among those which brought a change to the Employer Liability Act. His most noteworthy opinions are Hipolite Egg Co. v. United States 220 U.S. 45, in which a unanimous Court upheld the Pure Food and Drug Act of 1906, In Hoke v. United States, he concurred in upholding the Mann Act, a/k/a "White-Slave Traffic Act". However, four years later, he dissented from the Court's opinion in Caminetti v. United States, which held the act applied to private, noncommercial enticements to cross state lines for purposes of a sexual liaison. According to McKenna, the Act regulated only commercial vice, i.e., "immoralities having a mercenary purpose." While McKenna was generally quite favorable to federal power, he joined the Court's substantive due process jurisprudence and voted with the majority in 1905's Lochner v. New York, which struck down a state maximum-hours law for bakery workers, This decision carried broader implications for the scope of federal power, at least until the New Deal and the 1937 switch-in-time-that-saved-nine West Coast Hotel Co. v. Parrish. McKenna resigned from the Court in January 1925 at the suggestion of Chief JusticeWilliam Howard Taft. McKenna's ability to perform his duties had been diminished significantly by a stroke suffered 10 years earlier, and by the end of his tenure McKenna could not be counted on to write coherent opinions. Justice McKenna was one of 14 Catholic justices in the history of the Supreme Court. McKenna married Amanda Borneman in 1869, and the couple had three daughters and one son. McKenna died on November 21, 1926. in Washington, D.C.. His remains are interred at the city's Mount Olivet Cemetery.
