Military Police, also known as PM, are the uniformed preventive state police of the states and Federal District of Brazil. The Military Police units are the main ostensive police force at the state level and are responsible for policing and maintaining the public order. Their formations, rules and uniforms vary depending on the state. Investigative work and forensics are undertaken by the Civil Police of each state.

All state Military Police and Military Firefighters Corps are classed as reserve troops and ancillary forces of the Brazilian Army. In time of war (or other emergencies) the military police forces can be pressed into federal service. Thus are organized in a military manner, following military hierarchy and ranks and in case of crimes or misconduct, they are tried in state military courts instead of the common (or civil) courts. But they remain distinct from the provosts belonging to the other services within the Brazilian Military: the Army Police (Portuguese: Polícia do Exército, PE) for the Army, Air Force Police (Portuguese: Polícia da Aeronáutica, PA) for the Air Force and similar units in the Brazilian Marine Corps for the Brazilian Navy.

The Military Police was founded in 1809 by the Portuguese Crown with the Military Division of the Royal Police Guard in Rio de Janeiro, based on the model of the Gendarmerie created in France: a public security force that combined police and military functions. In most provinces they were named Public Forces (Portuguese: Força Pública) or Police Corps (Portuguese: Corpos Policiais). After the Proclamation of the Republic, these police forces were subject to state authorities, where they had a role not only in law enforcement, but also in warfare, to face the various revolts and rebellions during the period of the Old Republic. These "small state armies" had larger contingents than the federal military forces themselves — the Public Force of São Paulo, for example, had artillery and military aviation divisions — and were more loyal to state governments, especially local oligarchs and "colonels". The name "Military Police" was only standardized in 1946 under the regime of Getúlio Vargas, with the new Constitution of 1946 after the Vargas Era of the Estado Novo (1937-1945), which had the objective of limiting the military capacity of the Public Forces in order to focus on being exclusively police forces. All federated units adopted the term, with the exception of Rio Grande do Sul, which still maintains the name Military Brigade (Portuguese: Brigada Militar) in its police force.

In 2004 the National Public Security Force (Portuguese: Força Nacional de Segurança Pública) was created to handle major security crisis. The unit, which is composed of the most qualified Military Police personnel from all federal states, is deployed in cases of major security crisis to augment local security forces by the request of local authorities.

The first militarized police in Portugal (when Brazil was still a colony) was the Royal Police Guard of Lisbon (Portuguese: Guarda Real de Polícia de Lisboa), established in 1801; which was followed by the model of the National Gendarmerie (French: Gendarmerie Nationale) of France, created in 1791.

When the Portuguese Royal Family was transferred to Brazil, the Royal Police Guard of Lisbon remained in Portugal, and another equivalent was created in Rio de Janeiro, under the name of Military Division of the Royal Guard Police of Rio de Janeiro, in 1809.

With the abdication of Emperor Pedro I in 1831, the Regency held reformulations on the Brazilian Armed Forces. The Royal Guard Police of Rio de Janeiro was abolished, and replaced by the Municipal Guard Corps of Volunteers; a type of security force similar to the French National Guard. The same law allowed each province to establish its own Guard of Volunteers.

In 1834 Pedro I died in Portugal and this reduced the fear in Brazil of a reunification of the kingdoms. The Guard of Volunteers were then transformed into Province Police Corps, with professional troops. The Police Corps were created with the same structure as the Army, and to serve as reserve troops when necessary.