Kelly won renomination in the Democratic Party primary against Thomas J. Courtney, the Cook County state's attorney.

In the Republican Party primary, Green won a massive victory over former mayor William Hale Thompson.

By seeking election an additional four-year term, Kelly was running to have the longest uninterrupted mayoralty Chicago had ever seen.

Rebellious and reform-oriented Democrats united behind Thomas J. Courtney as a challenger to Kelly and the political machine.

Horner had been engaging in a political feud with Kelly and Chicago Democratic boss Patrick Nash.

As an assistant district attorney, Green had helped to construct the income tax evasion case which led to mobster Al Capone's imprisonment.

[1] Green's campaign, in a sense, was a four-month series of attacks on the Kelly-Patrick Nash political machine.

[9] On the eve of the election, Kelly received a further boost when former United States District Attorney George E. Q. Johnson declared in a radio address that he considered Chicago to no longer be a capital of crime, arguing that the city now led the nation in crime prevention, largely crediting Kelly and the city's police commissioner for this.