Fergusson was born and grew up in Albuquerque, New Mexico, then attended Washington and Lee University in Lexington, Virginia, graduating in 1911. Soon after leaving college, he took a job as a staff reporter for the Washington, D.C. Herald. After brief stints with newspapers in Savannah, Georgia and Richmond, Virginia, he returned to DC and joined the Washington bureau of the Chicago Record-Herald. He left the paper in 1915 to work as an assistant to the columnist Frederic Haskin. He married for the first time in 1919 ... the marriage ended in divorce a few years later. In 1923, he left journalism to devote himself full-time to writing.

Fergusson's second novel, Capitol Hill, drew heavily upon his experiences as a reporter. His protagonist, Ralph Dolan, works his way up through the newspaper trade, then switches to the business of public relations and lobbying, ending as the top lobbyist of a large industry association.

Virtually in parallel with Capitol Hill, Fergusson wrote The Blood of the Conquerors, the first of his historical novels set in New Mexico. Blood was also the first novel in a trilogy Fergusson titled, Followers of the Sun. The other books in this trilogy were In Those Days and Wolf Song.

Wolf Song is considered by most critics to be his best novel ... indeed, some have called it the finest novel of the American West. It tells the story of a mountain man, Sam Lash, loosely modelled on Kit Carson. Fergusson married for the second time in 1927, the year of Wolf Song's publication, but his wife died of pneumonia before the year ended.

He moved to Hollywood and worked intermittently as a screenwriter, earning credits on It Happened in Hollywood (1937) and Stand Up and Fight (1939). His primary focus remained on novel-writing, although it would be over 20 years before he returned to the subject of the West's past. His two novels of the 1930s dealt with contemporary themes, and Fergusson also published two works of non-fiction, Rio Grande and Modern Man: His Beliefs and Behavior.

Fergusson moved to Berkeley in the early 1940s, where he wrote an autobiographical book, Home in the West: An Inquiry into My Origins. He also returned to the subject of politics, this time as a work of non-fiction, People and Power: A Study of Political Behavior in America.

His last two novels, Grant of Kingdom and The Conquest of Don Pedro, dealt with earlier periods in the history of New Mexico. Fergusson consciously sought to correct what he saw as the fundamental flaw in conventional Westerns: "... not that its stories are melodramatic but that its heroes and heroines are lifeless."

Fergusson died in Berkeley, in 1971, at the age of 81.