In 1894 Friedrich-Wilhelms-Universitaet awarded him the degree DPhil with a thesis entitled "Ueber den Bau der Phalangidenaugen" ("On the structure of the eyes in the Phalangida").

He took up an appointment as First Assistant at the South African Museum and keeper of the terrestrial invertebrates collection (excluding insects) in 1896, under its new Director, W.L.

[2] He was the first South African zoologist to start a systematic study of spiders, devising keys and providing full descriptions of species.

[2] Up to that time Arthur Stanley Hirst (1883–1930), Pickard-Cambridge and R. I. Pocock of the British Museum had occasionally named spiders sent to them from South African sources.

Pocock especially was supplied with unknown specimens from Natal and Rhodesia, many coming from Selmar Schonland, the botany professor at Rhodes University.

South Africa is a fertile hunting ground for the study of Mygalomorphae or 4-lunged spiders, and both Purcell and R. W. E. Tucker who succeeded him, were drawn to this group, as was J. Hewitt.

William and Anna Purcell are an example of husband and wife collaboration in arachnology, the other well-known couple being George and Elizabeth Peckham from the States who worked on South African Salticidae.

[2] Some of his publications include:[6] On 24 March 1897, Purcell married Anna Cambier Faure,[7] who was a close South African friend of Olive Schreiner.