Born in New York, New York, McCormick attended St. Ignatius College, and read law to enter the bar in 1900. He was in private practice in Los Angeles, California from 1900 to 1905. He was an Assistant district attorney of Los Angeles County, California from 1905 to 1910, thereafter serving as a judge on the California Superior Court for Los Angeles County until 1921, and as an associate justice of the District Court of Appeals of California from 1921 to 1924.
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 Oscar A. Trippet. McCormick was confirmed by the United States Senate on February 11, 1924, and received his commission the same day. 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.
McCormick served as chief judge of the court from 1948 to 1951. He assumed senior status on September 1, 1951, serving in that capacity until his death.