 Thomason served from March 4, 1931 until his resignation on July 31, 1947, to take a seat on the federal bench.Thomason was nominated by President Harry S. Truman on April 24, 1947, to a seat on the United States District Court for the Western District of Texas vacated by Judge Charles Albert Boynton.He was confirmed by the United States Senate on June 3, 1947, and received his commission on June 5, 1947.