John Griffith was among the most prominent clergyman in industrial south Wales during the second half of the nineteenth century. He was rector of Aberdare from 1846 until 1859. From 1859 until his death in 1885 he was vicar of Merthyr Tydfil where he proved a strong supporter of workers' rights and, by the end of his life a supporter of the disestablishment of the Church of England in Wales. This reflected the way in which he gradually abandoned the strong Tory principles that he espoused at the beginning of his career at Aberdare. He died on 24 April 1885.
Griffith was born in 1818 or 1819 in Llanbadarn Fawr, Cardiganshire, the son of Thomas Griffith. He commenced his education at Ystradmeurig School, which was a popular choice amongst the gentlemen farmers of Cardiganshire for educating their sons. He proceeded to Swansea Grammar School and Christ's College, Cambridge, he was ordained a priest in 1843. After a short period as curate of Astbury in Cheshire, Griffith benefitted from the patronage of Sir Stephen Glynne, brother-in-law of W.E. Gladstone, and for a short time became family chaplain at Hawarden. However, a collapse in the family finances in 1846 made it necessary for Griffith to seek alternative employment.
At this time, Griffith had been writing to the Cardiff and Merthyr Guardian, using the pseudonym, Cambro Sacerdos, and in these articles drew attention to deficiencies that still existed within the church despite reforms undertaken in the 1830s. The articles came to the attention of the owner of the newspaper, the Marquis of Bute. Bute was not only an evangelical and supporter of church reform but also, as Lord Lieutenant of Glamorgan, concerned about the preservation of law and order within the developing industrial communities in the upland parts of the county. Under these circumstances, Griffith emerged as a candidate for the vacant parish of Aberdare which was endowed by the Marquis.
The parish of Aberdare was established in 1846 when it ceased to be part of the pre-industrial parish of Llantrisant, many miles to the south. The new parish was a large one, extending from Hirwaun in the north to Mountain Ash in the south, an area of some fifty square miles centred on the town of Aberdare. The whole area was expanding rapidly due to the opening of ironworks and collieries, with the population increasing by approximately 1,000 people each year. The only Anglican place of worship was the small and ancient St John's Church, while there were already at least fourteen substantial nonconformist chapels in the parish. It was only towards the end of his ministry at Aberdare that St John's Church became suitable for regular worship once again after a restoration costing £900. By that time however, Griffith had instigated the building of St Elvan's Church, commonly known as the Cathedral of the Valleys, which revitalised the influence of the Church in this industrial community.