Cox entered politics soon after opening his practice, winning his first race for elective office in 1908, for a seat on the Boston Common Council. The following year he won election to the state legislature, where he served nine annual terms, the last four as
Speaker of the Massachusetts House of Representatives. During these years he became politically associated with
Calvin Coolidge, who was Senate President and
Lieutenant Governor. Coolidge tapped Cox as his running mate for governor in 1918, and Cox served two one-year terms as lieutenant governor. Coolidge stepped back to run for
Vice President of the United States in
1920. Cox contributed to the
anti-immigrant sentiment in Massachusetts by characterizing discontented immigrants as a "motley array of questionable groups and influences". He won reelection in 1922, in another race against disorganized Democratic opposition. Although the state was in an economic downturn (an early whisper of the
Great Depression), with textile production dropping and wages down, his campaigns emphasized "economy and sound administration" in governance, terms which characterized Republican campaigns through the 1920s. In 1922, Cox defeated former
Mayor of Boston John "Honey Fitz" Fitzgerald by more than 60,000 votes. As governor, Cox was somewhat more progressive than Coolidge, advancing a variety of modest reforms. He increased schooling requirements and reduced working hours for children, allowed labor unions to instigate lawsuits against employers, and improved workmen's compensation coverage. He signed legislation restricting the ability of state banks to engage in speculative investments, and instituted a commission on finance and reform to oversee the state's finances. In the 1922 race, Cox claimed credit for reducing income taxes by $2 million and the state's debt by $12 million. Substantive reforms were typically buried by the legislature, which studied reform proposals but generally did not act on them. Cox opted not to run for reelection in 1924, supporting Lieutenant Governor
Alvan T. Fuller as his successor. ==Later years and family==