His work, covered the counties of Pembrokeshire, Carmarthenshire, Cardigan, Denbighshire, Montgomeryshire in Wales and Shropshire and Cheshire in England.

He was born at Overton-on-Dee, Flintshire, Wales, in 1815, the eldest son of Thomas Penson II, an architect and surveyor of Gwersyllt Hall near Wrexham, who had offices in Willow Street, Oswestry, and his wife Frances (nee Kirk).

[3] He was the brother of Thomas Mainwaring Penson, an architect noted for his railway stations and Tudor Revival architecture.

[3] Prompted by Queen Victoria's Osborne House which was completed in 1851, the Italianate style of architecture became popular in the second half of the 19th century.

Examples of Penson's use of the Italianate style include Llandovery Town Hall and the gate lodge to Nanteos.

The style was popular for country houses in Carmarthenshire and include the now-demolished Pant Glas at Llanfynydd and Gellideg at Llandyfaelog.