The family were Sandemanians, part of the same congregation as Michael Faraday, but Varley did not continue his association with the sect into adult life.

Varley was an astute businessman and the partnership that he formed with the 1st Baron Kelvin and Fleeming Jenkin to exploit their respective telegraphic inventions yielded large profits for the three men.

[3] He was sympathetic to the claims of Spiritualism and carried out investigations with fellow physicist William Crookes using a galvanometer to make measurements of the supposed phenomena.

His belief was based on the idea that because the rays were deflected in the presence of a magnet, these particles have to be considered carriers of an electric charge.

[citation needed] Varley had two sons and two daughters with his first wife, Ellen Cayley (née Rouse) (1837-1920), whom he married on 4 October 1855.

In 1904, Varley's elder son, also named Cromwell, was kidnapped along with Perdicaris by Mulai Ahmed er Raisuni, precipitating an international incident before both men were released unharmed.