[7] By the time he returned permanently to New Zealand in 1892, joining his father's merchandising firm, he was already collecting books.

Turnbull had a standing order with the London bookseller Bernard Quaritch, which was regularly updated to include more subjects.

An analysis of Turnbull's collecting history has been explored through his correspondence with book sellers in Australasia, the United Kingdom, America, and continental Europe.

[11] After his death, Turnbull's collection contained approximately 55,000 books, as well as manuscripts, photographs, paintings and sketches (the artefacts having already been given to the Dominion Museum).

Turnbull's Milton collection continues to be added to, by purchase and donation; a number of significant additions were made in the 1970s.