Sidney Barnsley trained as an architect in London with Richard Norman Shaw. Through his elder brother, Ernest Barnsley, he met Ernest Gimson. Between 1891 and ‘92, he was one of five architects including Gimson and William Lethaby who designed for Kenton & Company. In April 1893 the two Barnsley brothers and Gimson moved to Gloucestershire.
In their shared workshop at Pinbury Park, near Sapperton, Sidney Barnsley developed his carpentry skills. He made chests, cabinets and tables whose constructional details, cogged dovetails, dowels, and through tenons, were integral to the design. He combined rural carpentry techniques such as chamfering and chip carving with sophisticated carefully-proportioned designs. After the move to Sapperton in 1902 he continued to make all his designs in a workshop in his garden.
His architectural output was limited. His first commission, the Church of the Wisdom of God at Lower Kingswood, Surrey is an exquisite exercise in the Byzantine idiom.