Born in Somerville, Massachusetts, McCarthy received an Artium Baccalaureus degree from College of the Holy Cross in 1905 and a Juris Doctor from Boston University School of Law in 1908.
He was an assistant district attorney of Middlesex County, Massachusetts, from 1913 to 1915.
He was an Assistant United States Attorney for the District of Massachusetts from 1934 to 1947.
[1] McCarthy was nominated by President Harry S. Truman on January 13, 1949, to a seat on the United States District Court for the District of Massachusetts vacated by Judge Arthur Daniel Healey.
He was confirmed by the United States Senate on January 31, 1949, and received his commission on February 2, 1949.