The Main Guard first served as a guardhouse; in the 20th century, it functioned as a fire station, bath house, and government offices.

The Main Guard is a historic building in Gibraltar, the British Overseas Territory at the southern end of the Iberian Peninsula.

In 1748, a Gibraltar visitor who stayed at an inn on the Parade, a former name for John Mackintosh Square, wrote that the "grand guard house" was near his hotel and that it was "one of the neatest buildings" in the area.

[3] The 1830s painting (pictured above) by British artist Thomas Colman Dibdin (1810 – 1893) shows the Main Guard with officers stationed outside, as well as the nearby Exchange and Commercial Library on the eastern side of the square.

[8] Early 19th-century regulations in Gibraltar required that any inhabitant wandering in the streets after midnight without a permit was to be transferred to the Main Guard.

[12] The French painter Henri Regnault (30 October 1843 – 19 January 1871), a native of Paris, was a frequent visitor to the Main Guard in the late 1860s, as he was a friend of the officers.

[13] The artist (pictured at left) produced three paintings for the officers which, after being displayed at the guardhouse for many years, were removed for restoration and their current location is unknown.

Until late 1920, it was home to the Military Foot Police, and, from February 1921 to March 1938, the building served as the City Fire Station.