St Sulien's was a medieval parish church, belonging to the Deanery of Sub-Aeron. First mentioned in documents of 1281, its valuation was at that time equal to nearby St Peter's Church, Lampeter (NPRN 270). In 1833 the living was consolidated with Llanwnen vicarage, in the patronage of the Bishop of St Davids (to whom two thirds of tithes were appropriated, with the other third to the vicar). The church site is an elevated but sheltered one, set back from the C1038. The Nant Tawelan flows under a bridge some 10m west of the church. Some 200m south-west is an Iron Age concentric antenna enclosure (NPRN 405320), identified during RCAHMW aerial reconaissance in 2006. The curvilinear churchyard seems to have been enclosed by a 14ft wide ditch, traces of which were identified in the 1990s at adjacent Plas Newydd. An inscribed stone, Silian 1 (NPRN 419117) is built into the church's external south wall, and is thought to date to the fifth/sixth century. It is superimposed with a later linear latin cross. A ninth/tenth century decorated stone, Silian 2 (NPRN 275650) was first recorded in the churchyard in 1808 and moved into the church in 1960. In May 2013 a lost ninth/tenth century inscribed stone, Silian 3 (NPRN 419114) was rediscovered at a findspot (NPRN 419115) some 40m south of the church. Its pattern includes a linear Latin cross with a lozenge shaped ring at its upper end, and with stones at St David's Church, Llanllawer (NPRN 308778), St Tecwyn's Church, Llandecwyn (NPRN 43903) and St Tanwg's Church, Llandanwg (NPRN 43901) is one of only four definite examples in Wales. The churchyard was extended in the 1920s, its new boundary possibly spatially coterminous with a former outer enclosure boundary. A noteable grave is that of Julian Cayo-Evans (died 1995), a leader of the Free Wales Army. Silian School (NPRN 408825), some 70m south-west, was built in 1855-1856 as a Church school, and continued as such until until 1906 when management was handed to the Local Authority. Links between school and church continued, with Sunday School held there, and the school logbook of 1972 recording the pupils attending church on Ascension Thursday.

The pre-1840 church is known to have consisted of nave and chancel with west bellcote, and was described as an ancient ediface in 1833. The church was rebuilt in 1838-1840. It was again rebuilt in 1872-1873, to the designs of R.J. Withers, Chester, on the foundations of its predecessor. It is constructed of local silurian split-shale rubble, and consists of two-bayed nave, three-bayed chancel, north (lean-to) vestry and west bellcote with spired bell turret. The church's original late twelfth/early thirteenth century font, with four human masks in relief, is similar to those at St Patrick's Church, Pencarreg (NPRN 418382), St Llawddog's Church, Cenarth (NPRN 309895) (taken from St Tysilio's Church, Llandisiliogogo, NPRN 400361), St Mary's Church, Llanfair Clydogau (NPRN 402887) and St Llwchaiarn's Church, Llanllwchaearn (NPRN 301818). It now lies loose at the west end of the church. The external gabled west doorcase carries a ringed shaft up to the corbelled base of the bell turret. The chancel arch is also corbelled. The circular font dates to 1873. The timber roofs are open. There is a blocked fireplace in the south vestry wall. Three stained glass windows on the east wall (above the alter), the Stewart windows, were commissioned by the Stewart sisters in 1936. They commemorate father, John (first headmaster of Silian school, whose portrait hangs on the vestry wall), mother, Margaret, and brother, Jenkin William. Designed by A.E. Lemmon, Bromsgrove, they are notable as the only windows of their type in the area. Two north windows are by Celtic Studios, 1961, with the western one dedicated to the three Stewart sisters, and the eastern one to Isaac Parry Jones and wife, vicar of Silian (1930-1950). The window over the organ (south wall) is dedicated to Mary Ann Jones, church organist for 50 years. Electricity was installed in 1956, after which an electric organ replaced the former organ, which was removed to St Mary's Church, Maestir (NPRN 310150).

Sources include:
Cambria Archaeology, 2000, Ceredigion Churches, gazetteer, 48
Edwards, N, 2007, A Corpus of Early Medieval inscribed stones and Stone Sculpture in Wales
Lloyd, T, Orbach, J and Scourfield, R, 2006, The Buildings of Wales
Vousden, N, 2010, 'The Landscape of a Ceredigion Parish: charting the changing patterns and significance of land use in Silian', unpublished undergraduate dissertation, University of Wales Lampeter

N Vousden, RCAHMW, 6 February 2013