Ernest Aloysius O'Brien (July 1, 1880 – October 9, 1948) was a United States district judge of the United States District Court for the Eastern District of Michigan.

Born in Detroit, Michigan, O'Brien received a Bachelor of Arts degree from Detroit College (now University of Detroit Mercy) in 1898 and a Bachelor of Laws from Detroit College of Law (now Michigan State University College of Law) in 1905.

He was a Judge of the Circuit Court of Michigan in 1928, returning to private practice from 1928 to 1931.

[1] On February 26, 1931, O'Brien was nominated by President Herbert Hoover to a new seat on the United States District Court for the Eastern District of Michigan created by 46 Stat.

O'Brien served in that capacity until his death on October 9, 1948.