He married Ceil Baring-Gould in 1937.

He was creative director of Time magazine's circulation and corporate education departments from 1937 until his death. His paternal grandfather was Reverend Sabine Baring-Gould.

In 1955, Baring-Gould privately published The Chronological Holmes Sherlockian.Net: William S. Baring-Gould, an attempt to lay out, in chronological order, all the events alluded to in the Sherlock Holmes stories. Three years later, Baring-Gould wrote The Annotated Mother Goose: Nursery Rhymes Old and New, Arranged and Explained, with his wife, Lucile 'Ceil' Baring-Gould. The book provides a wealth of information about nursery rhymes, and includes often-banned bawdy rhymes.

In 1967, Baring-Gould published The Annotated Sherlock Holmes, an annotated edition of the Sherlock Holmes canon, its subtitle promising "The four novels and fifty-six short stories complete". The following year, Baring-Gould published The Lure Of The Limerick, a study of the history and allure of limericks; it included a collection of limericks, arranged alphabetically, and a bibliography. The book was republished in 1974.

Baring-Gould also wrote Nero Wolfe of West Thirty-fifth Street: The life and times of America's largest private detective, a fictional biography of Rex Stout's detective character Nero Wolfe. In this book, Baring-Gould popularised the theory that Wolfe was the son of Sherlock Holmes and Irene Adler.