He was the son of Thomas Penson the elder (c. 1760 – 1824), who had been the county surveyor for Flintshire from 1810 to 1814, but had been dismissed when the bridge at Overton-on-Dee collapsed.

In 1839, his wife inherited from her father Gwersyllt Hall or Hill near Wrexham, which Penson remodelled in Neo-Jacobean style, and which became their home.

[6] Among Penson's pupils were J. W. Poundley, who was to become the Montgomeryshire county surveyor in 1861, and the Welsh poet John Jones (Talhaiarn).

Penson designed a two-span cast iron arch bridge at Caerhowel in 1858 to replace a timber structure destroyed by floods.

Against his advice, a suspension bridge designed by James Dredge had been built in 1854, only to collapse four years later under the weight of three lime wagons, killing one man.

More particularly he seems to be copying Saint Salvator's Cathedral in Bruges, with buff (rather than the normal red) bricks and has pyramid capping on the pinnacles.

Saint Salvator's tower had been remodelled by Robert Dennis Chantrell following a fire in 1838, and this may provide a connection with Penson[13] The design is probably also influenced by Pugin's Roman Catholic St Chad's Cathedral, Birmingham, which is a slightly earlier example of Brick Gothic revival.

[16] The source for Penson’s terracotta appears to have been the brickworks associated with the Oswestry coalfield between Trefonen and Morda which were to come into the ownership of the railway engineer Thomas Savin.