In November 1905, city voters elected Langdon as district attorney of San Francisco, and in 1907 re-elected him to a second term. 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 RepublicanJames 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, along with special assistants Francis J. Heney, Hiram Johnson and Matt Sullivan. After his tenure as district attorney, Langdon entered banking, serving with several banks around Modesto and managing the property his wife had inherited from her first husband. In 1913, he served as the head of the StateBoard of Education. In 1915, he reentered law when Governor Hiram Johnson appointed Langdon a judge of the Superior Court of Stanislaus County. In December 1918, Governor William Stephens appointed Langdon presiding judge of the newly minted First District, Second Division, of the California Court of Appeal. In 1920, Langdon was elected to a full term. In November 1926, Langdon won election to a 12-year term as an Associate Justice of the Supreme Court of California, where he served the next nineteen years until his death in 1939. Langdon filled the unexpired term of William P. Lawlor, who died in office in July 1926, and whose seat was filled for three months by the appointment of Jeremiah F. Sullivan. From 1930 until 1939, treatise author Bernard E. Witkin served as Langdon's law clerk. In October 1939, the vacancy in Langdon's seat was filled by Governor Culbert Olson with the appointment of Phil S. Gibson. Among Langdon's notable cases is his 1930 dissent in the denial of a commuted sentence of convicted double murderer Ernest A. Dias. The majority of the court upheld the death penalty, but in dissent Langdon urged the governor to grant executive clemency on the basis of Dias' mental incompetence at the time of the killings.
Personal life
On April 20, 1908, he married Stanford-trained school teacher, Myrtie Conneau McHenry, a wealthy widow from Modesto, California. They had one son: Lawton William Langdon. His wife, Myrtie, also had two children from her first marriage: Lois Ann Langdon and Merl McHenry.
