A historian, Harlow's writing focused often on America infrastructure, including transportation and communication, and New York history.

During his time with the Company, he worked in Appalachia, where he created educational films about Appalachian people.

[1] Harlow shifted his writing to focus on history, documenting detailed, specialized books about various facets of American culture.

[1] He also wrote biographies, including being the official biographer of Eddie Foy Sr. and Jefferson De Angelis.

He also wrote biographies about Joel Chandler Harris, Bret Harte, Theodore Roosevelt and the Ringling brothers.

[1][3] A decade worth of Harlow's manuscripts are held in the collection of the University of Tulsa's McFarlin Library.