Barrett collected insects throughout much of Australia, sending many to entomologists in other parts of the world. He visited troops in northern Australia and New Guinea during World War II, lecturing on practical bush lore. Barrett wrote popular books such as Coast of Adventure, In Australian Wilds (1919), Pals (a boys' paper, 1920-28), the dozen Sun Nature Books (cheap, but attractive, introductory books) and edited and contributed to the Australian Children's Encyclopaedia.

Barrett married Florence Ellen ("Effie") nee Williams, a trained nurse, on 12 June 1911. Florence accompanied Charles on his travels to the Great Barrier Reef, the Nullarbor Plain and across central and northern Australia as 'assistant naturalist'. She was also actively involved in the Field Naturalists Club of Victoria, organising the Ladies' Committee that assisted with the wildflower shows. She died in October 1957.