He was an assistant district attorney of Los Angeles County, California from 1905 to 1910, thereafter serving as a Judge of the Los Angeles County Superior Court until 1921, and as an Associate Justice of the District Court of Appeal of California from 1921 to 1924.

[1] On February 7, 1924, McCormick was nominated by President Calvin Coolidge to a seat on the United States District Court for the Southern District of California vacated by Judge Oscar A. Trippet.

McCormick was confirmed by the United States Senate on February 11, 1924, and received his commission the same day.

He assumed senior status on September 1, 1951, serving in that capacity until his death on December 2, 1960.

[1] In 1929, President Herbert Hoover appointed McCormick as one of the eleven primary members of the Wickersham Commission on issues relating to law enforcement, criminal activity, police brutality, and Prohibition.