He was in private practice in Newark from 1937 to 1958, also serving as a private in the United States Army during World War II, from 1942 to 1943, and as a counselor and lecturer at the Rutgers Law School from 1954 to 1957.

He was chosen to be chief counsel to New Jersey Governor Robert B. Meyner in 1958, despite being a registered Republican.

[1] He served in this capacity until 1960, reportedly turning down a Superior Court appointment and instead returning to private practice.

[1] On February 21, 1973, Biunno was nominated by President Richard Nixon to a seat on the United States District Court for the District of New Jersey vacated by Judge Robert Shaw.

He assumed senior status due to a certified disability on March 23, 1982, serving in that capacity until his death on July 30, 1991, in Passaic, New Jersey.