The history of the church in Beith goes back a long way. The first signs of Christianity coming to what is now the parish of Beith were through St. Inan who is reputed to have come over from Iona, to which island St. Columba came from Ireland and set up a monestary. In those early days there was no building where the people could assemble to worship or to listen to St. Inan. He preached to the people on the Bigholm Hills. There is a rock formation known, even until today, as St. Inan's Chair, which, it is reputed, he used as a pulpit. Near St. Inan's Chair there is a stone, known as the Rocking Stone, (which no longer rocks), and is thought to have been the site of pre-christian worship. This is most probably true as the first christian missionaries in Scotland usually began their work as near as possible to the spot where pre-christian rites and ceremonies took place, evidence of this being Druid's graves near the Rocking Stone.
Later, although it is difficult to assess exactly when, a church was built on the site where the "Auld Kirk" still remains to this day. About the time of the Reformation a new church was built, being cruciform in design (built in the form of a cross). This, in later years, was extended and a new belfry erected. The bell, still there, having been gifted by Hugh Montgomery of Hessilhead. It was not until 1810 that a larger church was built-now known as the High Church-to accommodate the growing population of the parish.
Before this there was dissention in the church. The ordinary members began to become dissatisfied with the fact that the heritors (land owners) were the people who chose the minister for the parish. This was known as patronage and in many cases the local minister was under the thumb of the heritors. Thus it was that in 1761 some members broke away from the established church and built a church of their own in Mitchell Street and appointed a minister thereto. This was known as the United Presbyterian Church and carried on as such until 1917. It is an interesting sidelight that a minister from Mitchel Street church set up a United Presbyterian Church in Wellington Street in Glasgow which, after a number of years, became too small for the congregation and a new church was built in University Avenue, and to this day it is called Wellington Church.
In 1784 there was another break away from the established Kirk. The reason was that in the "Auld Kirk" there was not enough room for the worshippers, who were not allowed to use the pews of the heritors. Again a number severed themselves and built a "Relief" Church in Head Street and attached themselves to what had become the Free Church.
Later in 1843 there was further dissention and another splinter group broke away and attached themselves to the United Free Church and erected a building at the junction of the Bigholm Road and Wilson Street. This church was known as Hamilfield because it was built on ground given by the owners of Hamilfield estate. This church continued as a place of worship until 1916 when it was gutted by fire, the cause of the fire never having been officially established. In 1917 the three splinter groups came together and worshipped in Head Street church.
The shell of the burnt out Hamilfield Church was used as the nucleus for a new church. A chancel was added, a transept (which makes it semi-cruciform), a hall and other accommodation. The new church was opened and dedicated on the 20th January 1926. The cost of restoring the former Hamilfield church was £11000. In 1929 Trinity Church became part of the Church of Scotland when the union took place in that year.