Rev Pooley Shuldam Henry was minister of First Presbyterian Church in Armagh from 1826 to 1846, when he was appointed first president of the new Queen's College in Belfast. During his rather stormy ministry sixty families memorialised Armagh Presbytery to form another congregation and Third Armagh was recognised by the presbytery on 7 November 1837. The first minister Rev John Richard McAlister, originally from Garvagh, was installed on 13 June 1838 and services were held for a time in the old Methodist Church in Abbey Street.
The meeting-house on The Mall was opened for worship on 11 February 1840 by Rev Dr Henry Cooke and above the door is the inscription SCOTCH CHURCH MDCCCXXXVII. The year 1837 refers to the formation of the congregation rather than the opening of the building and the word Scotch reflects the Scottish roots of Presbyterianism in Ulster.
McAlister was very active and much used of God during the great Ulster revival in 1859. There were many converts at that time and the congregation flourished.