William Matthew Byrne, Sr. (July 10, 1896 – March 9, 1974) was a United States district judge.
Byrne was born in Bakersfield, California. He received an LL.B. from Loyola Law School in Los Angeles, California in 1929. He was in the United States Navy from 1917 to 1919. He was in private practice in Los Angeles from 1929 to 1943. He was a Member of the California State Assembly from 1925 to 1931. He was the Speaker pro tem from 1927 to 1931. He was a judge on the Los Angeles Municipal Court from 1943 to 1948. He was a judge on the Superior Court of California from 1948 to 1950.
Byrne was appointed as a federal judge to the United States District Court for the Southern District of California on September 27, 1950. Byrne received a recess appointment from Harry S. Truman to a seat vacated by J.F.T. O'Connor. Formally nominated on November 27, 1950, he was confirmed by the United States Senate on December 13, 1950, and received his commission on December 21, 1950. He served as Chief Judge from 1965-1966. He assumed senior status on June 30, 1966.
Byrne was reassigned to the United States District Court for the Central District of California on September 18, 1966.
Byrne's service was terminated on March 9, 1974, due to his death.