He was an assistant attorney general of the United States Department of Justice from 1933 to 1935.

[1] He was the first Knight of Columbus to be made a judge in Massachusetts.

[2] Sweeney was nominated by President Franklin D. Roosevelt on August 20, 1935, to a seat on the United States District Court for the District of Massachusetts vacated by Judge James Arnold Lowell.

He served as Chief Judge from 1948 to 1965 and as a member of the Judicial Conference of the United States from 1958 to 1961.

Sweeney served in that capacity until his death on November 5, 1966.