John Gillon was born in June 1816 in the Parish of Ahamlish in County Sligo. He was educated at St Patrick's College, Maynooth. He was then transferred to Scotland where he was ordained on the 13th March 1842 at St Andrew's Cathedral Dundee by Bishop Andrew Carruthers, Vicar Apostolate of the Eastern District of Scotland as the Archdiocese of St Andrews and Edinburgh before the restoration of the hierarchy was then known.

His first appointment was as assistant Priest at St Andrew's Cathedral in Dundee where he was to serve between 1842 and 1845. Then he was appointed as the founding Parish Priest of St Machan's, Lennoxtown where he was to serve for 21 years until 1866.

During this time St Patrick's Kilsyth had no Priest of it's own as St Patrick's Kilsyth as a parish was only founded by Fr John Galvin in 1865. Due to the large and growing Catholic population, Kilsyth became a Mission Station serviced from the local mother church of St Machan's Lennoxtown. Kilsyth was not alone in this regard as St Machan's was local mother church to a number of other Mission Stations notably Kirkintilloch, Strathblane, Balfron, Milngavie and Blanefield - a massive geographic area - which meant only irregular attendance by a Priest was possible.

It was Fr John Gillon who offered the first recorded post Reformation Mass in Kilsyth Christmas Day 1847. This is less than 2 years after he was asked to found the Parish of St Machan's in Lennoxtown and service such a massive area covering multiple Mission Stations. It is also recorded regarding the first post Reformation Mass in Kilsyth that "such was the intolerance of the inhabitants, that finding a place in which to offer the Holy Sacrifice of the Mass was next to impossible, but eventually a house in Charles Street was found before a more permanent location, Arnot's Hall, could be hired." Source - Catholic Directory of 1848.

In 1866 Fr Gillon was transferred to St Andrew's Cathedral Dundee where he served until 1870. He was then transferred to the Church of St Thomas of Canterbury in Arbroath, Angus for a short period before moving to his final Parish, St Francis Xavier's Falkirk.

Tragically Fr Gillon was to die from Typhus fever which he contracted whilst visiting the sick. He died on the 15th March 1871 at the age of 55 after serving almost exactly 39 years as a Priest. He is buried in Falkirk amongst his parishioners and the other victims of Typhus to which he was ministering at the time.