St Mark's Church is situated within a former wooded area, which is now an irregualarly shaped churchyard. Prior to the 1890s, Brithdir and Islaw'r dref was a township of Dolgellau. The independent parish of Brithdir and Islaw'r dref came into being in 1894, and a new church was accordingly built. It replaced St Paul's as the place of worship for parishioners living in the Caerynwch and Brithdir area. The width of the main gate leading into the churchyard was intended to accomodate the passage of carriages through it. The church was designed by Henry Wilson, with the assistance of the young architects H. L. North, Arthur Grove and C. H. B. Quennell, between 1895 and 1898 in memory of Rev. Charles Tooth, the founder of the Anglican Church in Florence (who had died in 1894). Although now encompassed by rhododendron, it is one of the best examples of the genre and remains largely as it was first designed. It is intended to be elemental and severe, and to 'appear as if it had sprung out of the soil, instead of being planted down on it'.

The Church is a Grade I listed building, and is considered one of the pre-eminent churches of the Arts and Crafts Movement. The interior decoration and fittings are arguably the most complete and high-quality Arts and Crafts work in Wales. These include, amongst other outstanding features, a richly decorated circular lead font based on a design by W. R. Lethaby, a decorated copper altar made by the 'lost wax' process that features a drawing of the Annunciation with the Virgin and dove to the left faced by a kneeling angel-child and, to the extreme right, two sombre figures of Charles Tooth and his guardian angel. The pulpit is of beaten copper with three faces each featuring a wreath encircling grapes. The ends of the stalls have animals carved by Arthur Grove. The nave doors are built from oak and teak in chevrons, the points ofwhich have tiny sparkling crowns of mother-of-pearl.

Sources include:
Cadw, Listed Buildings Database
Corbett Harris, M, September 1976, 'Alien Styles in Harmony' in Countylife
Haslam, Orbach and Voelcker (2009), The Buildings of Wales: Gwynedd. Pevsner Architectural Guide, page 561.

RCAHMW, 9 October 2009.