Stephens worked along the Mississippi River as a surveyor. Settling in Los Angeles, he was a traveling salesman before becoming manager of Carr & Stephens Grocers. That was the springboard from which he launched a career in politics. Stints on the Board of Education and president of the Chamber of Commerce led to a seat on the Water Commission, where he advised on the building of the city's aqueduct. He served as interim mayor for less than a week in March, 1909, then became a 3-term Congressman.

He was appointed Lieutenant Governor of California by Governor Hiram Warren Johnson to replace the late John Morton Eshleman. Stephens became California's 24th Governor on March 15, 1917 when Johnson resigned to take his seat in the United States Senate, and served the remainder of Johnson's term.

World War I started a few months after Stephens took office; his administration was the target of numerous threats. After the governor's mansion was bombed in December 1917 (the Industrial Workers of the World was blamed), Stephens led the campaign for the passage of a criminal syndicalism law. In 1918, he became the first acting governor to be elected in his own right. The only sitting Governor to be admitted to the Bar, Stephens opened a practice after his reelection bid failed.