The Missouri Volunteer Militia (MVM) was the state militia organization of Missouri, before the formation of the Missouri State Guard in the American Civil War.
Prior to the Civil War, Missouri had an informal state militia that could be called up by the governor for emergencies or annual drill "in accordance with the Missouri State Statutes of 1854." Larger militia elements, such as brigades or the element employed in the November 1860 Southwest Expedition of James Montgomery, were composed of independent regularly drilling volunteer companies, such as the St. Louis Grays, the National Guards, and the Washington Blues. Each of these companies wore its own distinctive, and highly ornate, uniform. Antebellum esprit de corps was enhanced by drill competitions among the independent companies.
During the 1861 secession crisis, pro-secession Missourians sought to use the state militia to their advantage. On 13 February 1861, General Daniel M. Frost formed five new MVM companies composed entirely of pro-secessionist "Minutemen".
On 21 March 1861, the Missouri Constitutional Convention voted against secession, killing any possibility of secession by political action.
Governor Claiborne Jackson, a crypto-secessionist, then called up part of the MVM under Frost, and posted them just outside St. Louis, with the intent of seizing the city by force. This alleged plot was thwarted on 10 May 1861 when the MVM force was surprised and captured by unofficial Unionist Saint Louis Home Guard, a paramilitary arm of the Unconditional Union Party organized by Francis Preston Blair, Jr., and led by U.S. Army officers including Nathaniel Lyon, during the so-called Camp Jackson Affair.