Today's district of Münnerstadt, located in the Lauertal valley to the east of Münnerstadt and Althausen, appears very early on in documents dating back to 899 and 999 and appears to have originally belonged to a royal estate, changed hands several times in the Middle Ages and was finally sold in 1217 mainly to Bildhausen Abbey, on which it remained dependent for centuries until the dissolution of the Cistercian abbey in 1802 in the course of secularization. The population of the small village lived from agriculture, farming, sheep and cattle breeding, as well as wine growing, which was increasingly replaced by beer brewing in the 17th century. However, the modest prosperity possible on this basis was repeatedly destroyed by marauding troops and war contributions. This was especially true during the turmoil of the Thirty Years' War, but also during the Seven Years' War and the Napoleonic campaigns at the beginning of the 19th century.
During the Bavarian period from 1814, Brünn belonged to the Münnerstadt district court, and later from 1862 to the Bad Kissingen administrative district. In the 19th century, the municipality and its population were repeatedly unable to raise the necessary funds to pay for their municipal duties. The village retained its old-fashioned and poor appearance until the second half of the 20th century, even though electrification had already been introduced in the 1920s. Only land consolidation, connection to the central water supply in 1970, incorporation into Münnerstadt in 1972 and extensive village renewal at the end of the 1970s "were to awaken Brünn from its millennium slumber and give the village a contemporary look", as one chronicler wrote. While the local school was closed in 1966, first to Poppenlauer and later to Münnerstadt, the kindergarten for the districts of Brünn, Althausen, Fridritt, Wermerichshausen and Kleinwenkheim has been run by a specially founded kindergarten association since 1974.
In July 2000, the parish of Brno celebrated the 600th anniversary of its local church dedicated to St. Sebastian, which was last extended in 1957 and fitted with three new bells the following year.