Knox was educated at the academies in Pembroke and Pittsfield, New Hampshire, became a teacher, and established an academy in Kingston, New Hampshire. In 1860 he went to Colorado to seek gold, and there became a reporter, and afterwards a city editor of the Denver Daily News and correspondent for various eastern newspapers. He went in the beginning of the civil war to the southwest, and served as a volunteer aid in two campaigns. He sent letters to the New York Herald and, after receiving a wound in a skirmish in Missouri, went to New York to become a journalist and general writer.
In 1866 he went on a journey around the world as a newspaper correspondent, the beginning of his life as a traveller to many places, including Siberia. Knox wrote forty-six books between 1865 and his death in 1896. Seven of these were republished with different titles. One of his most successful endeavors was The Boy Travellers series, comprising
Note: M&M attributes the anonymously published novel Lady Hetty: A Story of Scottish and Australian Life
(q.v.) (1875) to Knox, however it has since been established that John Service (q.v.) is the author.