The Christian Community in Penicuik may well have its beginnings in the missionary work of St. Mungo (Kentigern) in the latter part of the 6th. century. There are documented references about a church being here by the 12th. century. Indeed in 1296 the local priest Walter Edgar along with the Laird, Hugh de Penicok, had to swear loyalty to Edward 1 at Berwick during the Scottish wars of independence. The church ruins in the cemetery are largely the pre-reformation building as it evolved and was added to (as late as 1733 Sir John Clerk added an aisle to the building). The tower still holds a 5 cwt. bronze bell gifted and dated 1680. Shockingly this is also the site of the 1629 witch burnings, fueled by the hysteria set in motion by an insecure King James VI, misguided religious leaders and overly diligent civil authorities.

The foundation stone for a new church was laid on August 15th. 1770 in the yard of the Schoolmaster's house. Built in the fashionable neoclassical style, it was a 'T' shaped building with an impressive portico surmounted by a nicely incised Cross. Some time later some locals tried to pull down, what they considered a 'papish' symbol (the Cross), but fortunately they never succeeded.

Although added to, throughout the 19th. century, it is basically the same Church building used by the St. Mungo's congregation today. A pipe organ by Miller of Perth was installed in 1884 and exists to this day. The clock in the pediment originally placed in 1884 has been replaced by modern workings—a gift from the British Legion.

St. Mungo's remains a working Church to this day