He received a Juris Doctor from the Ohio State University Moritz College of Law in 1952.

He was a judge of the Franklin County, Ohio Municipal Court from 1966 to 1968.

[3] Duncan was nominated by President Richard Nixon on May 1, 1974, to a seat on the United States District Court for the Southern District of Ohio vacated by Judge Carl Andrew Weinman.

[3] Following his resignation from the federal bench, Duncan returned to private practice with the firm of Jones Day Reavis & Pogue.

[2] Duncan was the first African-American elected to judicial office in Franklin County the first to serve on the Ohio Supreme Court, the first to serve on the United States Court of Military Appeals, and the first appointed to the federal bench in Ohio.