After the war, he remained in New Orleans as a Treasury agent.
Congress and death
He was elected as part of Louisiana's next congressional delegation after the state was readmitted to representation. He took his seat on July 18, 1868, and died on August 26, 1868.
The special election to succeed Mann was won by John Willis Menard, the first African American ever elected to Congress, but the House of Representatives declined to seat him.