The MO was established on 7 October 1944 by the Polish Committee of National Liberation under Chief Commander Franciszek Jóźwiak to police Red Army controlled areas of Poland during World War II.

Milicja had been adapted from the cognate term militsiya used in the Soviet Union, itself derived from militia with its etymology from the concept of a military force composed of ordinary citizens.

The MO was used to establish the authority of the PKWN in areas of Poland that came under control of the Red Army as it pushed through the country into Nazi Germany.

Its main fragment read as follows: I solemnly vow ...- to faithfully serve the Fatherland, the Party and People's Authority and to protect the law, order and public safety.The first chief commander of MO was Franciszek Jóźwiak.

In the years 1944–1948, the Citizens' Militia was used to fight cursed soldiers' ', as well as servicemen of the Ukrainian Insurgent Army and German Werwolf elements.

The ZOMO motorized riot troops, which played the most visible role in quelling demonstrations in 1980 and 1981, were reduced in size somewhat by the early 1990s and renamed Preventive Units of the Citizens' Militia (Oddziały Prewencji Milicji Obywatelskiej—OPMO).

OPMO forces are restricted to roles such as crowd control at sporting events, ensuring safety in natural disasters, and assisting the regular police.

Largely staffed by industrial workers who gained substantial privileges by monitoring their peers in the workplace, ORMO was the object of extreme resentment throughout the 1980s.