Cavanaugh was born on January 28, 1947, in Orange, New Jersey. He was raised as an Irish Catholic.^[1] Cavanaugh was educated at Morehead State University (Bachelor of Arts, 1969) and Seton Hall University School of Law (Juris Doctor, 1972).^[1] Cavanaugh teaches at Seton Hall as a member of the law school's adjunct faculty.^[1]

Cavanaugh began his legal career as a law clerk to Judge Francis W. Hayden in the New Jersey Superior Court (1972–73).^[1] He was then an Assistant Deputy Public Defender for the New Jersey Office of the Public Defender (1973–77) before entering private practice in various law firms in New Jersey (1977–92).^[1] Cavanaugh's private practice includes his partnership at the law firms of McCormack Petrolle & Matthews (1992), Whipple Ross & Hirsh (1987–92) and Tompkins McGuire & Wachenfeld (1984–87). He also served as a partner (1980–84) and associate (1977–80) at Lum Biunno & Tompkins. Cavanaugh was the Borough Prosecutor for the Borough of Caldwell (1988–89).^[1]

On May 3, 2000, Cavanaugh was nominated by President Bill Clinton , to a seat on the United States District Court for the District of New Jersey, which had been vacated by Judge Alfred M. Wolin.^[1] Cavanaugh was confirmed by the United States Senate on July 21, 2000, and received commission on September 20, 2000. Cavanaugh was formerly a United States magistrate judge of the same district (1993–2000).^[1] His service terminated on January 31, 2014, due to retirement.

• Dennis M. Cavanaugh at the Biographical Directory of Federal Judges, a publication of the Federal Judicial Center.