It was built between 1854 and 1856 to replace an earlier church in the parish, also dedicated to St Gwenllwyfo, which needed repair and had become too small for its congregation.

The new church was built nearer to the Llys Dulas estate, whose owner contributed £936 towards the total cost of £1,417, rather than near the area where many of the parishioners lived.

In 1876, Sir Arundell Neave (who had married into the family that owned Llys Dulas) donated 27 panels of 15th and 16th-century stained glass that had once belonged to a Flemish monastery.

[3] St Gwenllwyfo's Church stands in a churchyard on a sloping site on the west side of a rural road, about 0.5 miles (0.8 km) from the beach at Dulas, in the north-east of Anglesey, Wales.

[4][8] The largest donation towards the new parish church (£936)[n 2] came from Gertrude, the widow of William Hughes, 1st Baron Dinorben (died 1852), owner of Llys Dulas.

[3] Gertrude, whose husband had become rich from copper mining on Anglesey at Parys Mountain, also rebuilt the main house of Llys Dulas in the mid-1850s; it was demolished in 1976 after becoming derelict.

[9] Her daughter and heiress Gwyn Gertrude Hughes laid the foundation stone on 14 September 1854, using a silver trowel and ebony mallet.

A box placed underneath the stone contained a Bible, a prayer book, a document with details of the event and an example of every British coin minted in that year.

[1] The church, designed in the Gothic revival style, is built from rubble masonry dressed with gritstone, and has a slate roof.

Other windows in the nave and chancel contain saints or depictions of incidents in Christ's life (including one of Jesus wearing a straw hat after his resurrection, said to be "very rare").

[3][4][9] The church has a number of other memorials from the 19th and 20th centuries, commemorating members of the various families associated with Llys Dulas (Neave, Hughes and Dinorben).

The nave has three funerary hatchments (black diamond-shaped boards displaying the deceased's coat of arms) for Lord Dinorben, his wife Gertrude, and Sir Arundel Neave.

Cadw (the Welsh Assembly Government body responsible for the built heritage of Wales and the inclusion of Welsh buildings on the statutory lists) also notes the church's "fine collection of 15th- and 16th-century Flemish stained glass panels", which it says is the "second largest such collection in the world", and the 17th-century brass plaque.