John Lanneau "Johnny Mac" McMillan (April 12, 1898 – September 3, 1979) was a United States representative from South Carolina.

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

He was selected to represent the United States Congress at the Interparliamentary Union in London in 1960, and in Tokyo in 1961.

"[1] He is still the longest-serving congressman in South Carolina's history, and only Strom Thurmond and Ernest Hollings represented the state longer at the federal level.

He resided in Florence, South Carolina, where he died in 1979; interment was in the McMillan family cemetery, Mullins.