Born in Kensett, Arkansas, Mills began a legal career after attending Harvard Law School.

[clarification needed] As the youngest chairman of the Ways and Means Committee, Mills was the Congressional architect in establishing Medicare.

Mills served as the 29th county judge of White County between 1935 and 1939, and began small Medicare-like, county-funded program, with a $5,000 fund to pay medical bills (equivalent to $110,000 in 2023),[2] prescription drugs which were sold at cost, and hospital treatment for the indigent which were lowered to $2.50 per day (equivalent to $55 in 2023),[2] as well as have doctors see qualified patients free of charge.

Patients were qualified for the program through petitioning the local justice of the peace, who in turn made a recommendation to Mills as county judge.

He was a signatory to the 1956 Southern Manifesto opposing the desegregation of public schools ordered by the Supreme Court in Brown v. Board of Education.

However, Mills was never a segregationist personally: always a strong advocate for inclusion, his longest and closest aide was Walter Little, a black man from North Carolina.

Mills expected correctly that health care costs would continue to rise dramatically over time and, thus, would bankrupt Social Security.

He saw Social Security, Medicare, and Medicaid as programs that people need to rely on and it would be economically, psychologically, and politically devastating to terminate.

[7] Mills was drafted by friends and fellow Congressmen to make himself available as a candidate for president of the United States in 1972 in a few of the Democratic primaries.

He was not strong in the primaries and won 33 votes for president from the delegates at the 1972 Democratic National Convention, which nominated Senator George McGovern.

Despite the scandal, Mills was re-elected in November 1974 in a heavily Democratic year with nearly 60% of the vote, defeating Republican Judy Petty.