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Born in Marion, North Carolina, Erwin served in the United States Army during World War II, from 1943 to 1946, achieving the rank of Sergeant. He received a B.A. from Johnson C. Smith University in 1947, and an LL.B. from Howard University School of Law in 1951. While at Johnson C. Smith University, Erwin was a member of the Alpha Epsilon Chapter of Kappa Alpha Psi Fraternity.
He was in private practice in Winston-Salem, North Carolina from 1951 to 1977. Erwin served on his local school board in Winston-Salem, North Carolina (1961–68), on the North Carolina State Board of Education (1971–77), and was elected to two terms in the North Carolina Senate as a Democrat. In 1977, Governor Jim Hunt appointed him to the North Carolina Court of Appeals. In 1978, the voters of the state elected him to continue as an Appeals Court judge.
Federal judicial service
On June 11, 1980, Erwin was nominated by President Jimmy Carter to a new seat on the United States District Court for the Middle District of North Carolina created by 92 Stat. 1629. He was confirmed by the United States Senate on September 29, 1980, and received commission on September 30, 1980, thereby becoming the first black federal judge in North Carolina. Erwin later became chief judge of the United States District Court for the Middle District of North Carolina from 1988 until he assumed senior status on September 22, 1992. He served in that capacity until his death, in Winston-Salem.