He wrote articles for the Woolhope Naturalists' Field Club, the Archaeologia Cambrensis,[11] the Brecknock Society and others.

He focused on archaeology, local history, Welsh place names and the folklore of Breconshire and Radnorshire.

[23] He wrote a book entitled "Hay and Neighbourhood",[24][25] which revealed that churches once had door flaps for cats and dogs e.g. the south porch of St. Mary the Virgin, Brecon.

With a fellow member of the Woolhope club (i.e. George Marshal FSA) they carried out a partial excavation.

The also found artefacts including a Roman coin (Crispus A.D. 317–326), wire-wound Romano-Egyptian blue beads and Beaker pottery with flint flakes.

Cadw describe the long barrow as of "national importance for its potential to enhance our knowledge of prehistoric burial and ritual practices".

In conjunction with the Woolhope club, William conducted many local archaeological activities including a brief excavation on Llanthomas Castle Mound.

In 1911, the surviving Thomas family members resided temporarily in the Llanigon vicarage as guests of William as they awaited repairs to their home, Llanthomas hall.