Historic Ordnance Survey mapping (1889 and 1901) shows a tannery (NPRN 43841) on this site. The Holy Cross Catholic Church church was opened in 1952, and was registered for solemnising marriages in 1956. The Catholic community at Gellilydan originated from the families of Irish workers who came to work on the hydroelectric scheme at Trawsfynnydd in the 1920s. After the completion of the scheme two Irish Catholic families remained in the area. Catholic priests rarely visited the area, and the families were obliged to travel considerable distances in order to receive Catholic ministry. The Catholic community in the area grew, and at the time the church was opened its congregation numbered some 600.

The church is a Grade II listed building, formerly a tannery dating to the late eighteenth century. The building is constructed of mortared rubble stone, and has a slate roof. It consists of a four-bay linear range, with each bay articulated by a tall narrow window with slate sills. A stained glass window is set in the circular light of the south-west gable apex. Below this is the entrance porch, which is a later extension. The porch has a doorway in its north-west wall, with a four-light window with slate sill and lintel in its south-west wall. A low extension was built at right angles to the north-west wall. It comprises a single storey range with three six-pane windows, a slate roof and grit rendered walls.

Sources include:
Cadw, Listed Buildings Database
Ordnance Survey, 1889, first edition 25 inch
Ordnance Survey, 1901, second edition 25 inch
www.oocities.org/gellilydan/story.htm
www.london-gazette.co.uk/issues/40751

N Vousden, RCAHMW, April 2012