When Roosevelt learned of Cox's intentions, he pre-empted them by agreeing to a similar proposal from Missouri Senator Harry Truman.

Cox was appointed and then elected judge of the superior court of the Albany circuit and served from 1912 until 1916, when he resigned and unsuccessfully challenged the incumbent, Frank Park, for the Democratic nomination to represent Georgia's 2nd congressional district in the 65th Congress.

He was part of a series of conservative Democrats and Republicans who held the chairmanship of the U.S. House Committee on Rules from 1935 to 1961, which then prevented the passage of civil rights legislation.

"[4] In 1943, Cox sponsored and chaired a select committee whose mission was to investigate the Federal Communications Commission (FCC).

However, it was revealed that shortly before the investigation began, Cox had been paid to represent a private party seeking favorable action from the FCC.

[9] In the 82nd Congress, his final term, Cox was chairman of the United States House Select Committee to Investigate Tax-Exempt Foundations and Comparable Organizations.