Mordecai Baldwin Oliver (October 22, 1819 – April 25, 1898) was an attorney and two-term U.S. Representative from Missouri from 1853 to 1857.

Born in Anderson County, Kentucky, Oliver attended the common schools and then studied law.

He was admitted to the bar in 1842 and commenced practice in Richmond, Missouri.

Oliver was elected as a Unionist Secretary of State of Missouri in 1861.

He resumed the practice of law in St. Louis, Missouri, and served as judge of the criminal court from 1889 to 1893.