[4][5] In his youth Sonnenschein was apprenticed to the London publishers and book importers Williams and Norgate.

[8] The firm also acquired a reputation for publishing radical works, including those of George Bernard Shaw,[9] Karl Marx, and Edward Carpenter.

[10] In 1902 he left Swan Sonnenschein to work as senior managing director at the publishing house George Routledge & Sons.

[12] He was one of six children of Adolphus (Adolf) Sonnenschein, a teacher and writer originally from Moravia (now the Czech Republic) and his first wife, Sarah Robinson Stallybrass.

In 1917, responding to increasing anti-German hostility in Britain during World War I, he dropped his Germanic-sounding surname "Sonnenschein" and adopted his mother's maiden name, being thereafter known as "William Swan Stallybrass".