Mitchel had gained a reputation as a reformer and opponent of Tammany Hall for his investigations into corruption in city government.

After incumbent mayor William Jay Gaynor died on September 10, 1913, from complications stemming from his attempted assassination in 1910, Mitchel won the general election in a landslide over Democratic nominee Edward E. McCall and Socialist nominee Charles Edward Russell and became the second youngest mayor in New York City history.

His focus on national and international issues, as well as his frequent socialization with the city's elite, further eroded his popularity, as voters saw him as out of touch with local concerns.

Morris Hillquit, a leading socialist from Manhattan, co-authored the national party's St. Louis Manifesto, which proclaimed, The Socialist Party of the United States in the present grave crisis solemnly reaffirms its allegiance to the principle of internationalism and working-class solidarity the world over, and proclaims its unalterable opposition to the war just declared by the Government of the United States.

Bennett declined to withdraw from the race, and attempts to find a compromise anti-Tammany candidate failed, leading Mitchel to wage an independent campaign for re-election.

The Socialist Party, which drew heavy scrutiny from the federal government following the Russian Revolution and First Red Scare suffered crippling losses in the following years.

Morris Hillquit, who remained with the party he had helped to found, ran again for mayor again in 1932, received an eighth of the vote, and died the following year.