He was an Assistant United States Attorney of the District of Arizona in 1943.
He returned to private practice in Phoenix, Arizona from 1947 to 1952, and was chief counsel to the Arizona Code Commission from 1951 to 1952.
[1] On July 3, 1952, Walsh was nominated by President Harry S. Truman to a seat on the United States District Court for the District of Arizona vacated by Judge Howard C. Speakman.
He served as Chief Judge from 1961 to 1972, and assumed senior status on July 9, 1976.
[1] The James A. Walsh United States Courthouse in Tucson, Arizona was renamed in Walsh's honor in 1985.