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Langdon was born in Alameda County to William and Annie Langdon. Langdon attended local public schools, and graduated from the California State Normal School to become a teacher, while also entering the state bar to become a lawyer in 1896. Langdon served as vice principal and principal at schools in San Leandro, Fresno, and San Francisco, eventually becoming the city's school superintendent in 1902. In 1905, city voters elected Langdon as district attorney of San Francisco.
A popular district attorney, Langdon was nominated by the Independence League as its choice for governor in the 1906 elections. Langdon's presence as a strong third party candidacy won over 14 percent of the vote, proving to be a spoiler vote in a tight race between Democrat Theodore A. Bell and Republican James Gillett.
In 1907, one year after the aftermath of the San Francisco earthquake, Langdon carried out the successful prosecutions both of Mayor Eugene Schmitz and political machine operator Abe Ruef for bribery and extortion. After one term as district attorney, Langdon entered the world of banking, serving in a number of positions with several banks around Modesto. In 1915, Langdon reentered law, becoming a judge in the California Court of Appeals. In 1927, he was appointed as a judge to the Supreme Court of California, where he served the next nineteen years of his life until his death in 1939.
- Leonard, John William. Who's Who in Finance and Banking: A Biographical Dictionary of Contemporaries, 1920-1922. Joseph & Sefton, New York (1911), 1922.