In 1936, he published a critical edition of military-historical documents from the archives of the Duke of Cumberland at Windsor Castle.

He pursued a selective policy in the acquisition of new books, but contributed greatly to opening up and expanding the archival holdings.

Pargellis was interested in literary studies, supporting the journal Poetry with donations from the library during a period of financial difficulty in the 1940s.

Pargellis was one of the founders of the Hounds of the Baskerville (sic), a Sherlock Holmes society in Chicago affiliated with The Baker Street Irregulars, and gave the group its name.

After the death of his first wife, he married Mabel Spence Erler, who had worked at the library for 38 years and was head of the Technical Services Department.