She was a law clerk to Judge Lewis Render Morgan of the United States Court of Appeals for the Fifth Circuit from 1975 to 1977.

She was a member of the U.S. Attorney General's Advisory Committee on Sentencing Guidelines from 1988 to 1990 and was a Special Counsel to the U.S.

[2] On December 19, 2013, President Barack Obama nominated Carnes to the United States Court of Appeals for the Eleventh Circuit that was vacated by Judge James Larry Edmondson, who assumed senior status on July 15, 2012.

[5] On July 16, 2014, Senate Majority Leader Harry Reid filed a cloture motion on Carnes' nomination.

On July 17, 2014, the United States Senate invoked cloture on her nomination by a 68–23 vote.