Clifford Patrick O'Sullivan (December 8, 1897 – October 7, 1975) was a United States federal judge.
Born in Chicago, Illinois, O'Sullivan received an LL.B. from Notre Dame Law School in 1920. He was in private practice in Port Huron, Michigan from 1920 to 1924, and then in Chicago, Illinois until 1926, returning to Port Huron until 1957.
On June 6, 1957, O'Sullivan was nominated by President Dwight D. Eisenhower to a seat on the United States District Court for the Eastern District of Michigan vacated by Arthur A. Koscinski. O'Sullivan was confirmed by the United States Senate on August 5, 1957, and received his commission on August 7, 1957.
On January 14, 1960, Eisenhower nominated O'Sullivan for elevation to a seat on the United States Court of Appeals for the Sixth Circuit vacated by Charles Casper Simons. O'Sullivan's elevation was confirmed by the United States Senate on March 10, 1960, and he received his commission on March 12, 1960. He assumed senior status on September 27, 1969, serving in that capacity until his death, in 1975.