Slusser was born in San Francisco in 1939, the son of salesman Raymond Leroy Slusser and Edlo Mildred Raerth. He attended University of California, Berkeley where he studied both philosophy and English. Slusser, a member of Phi Beta Kappa, graduated summa cum laude in 1961 and then attended University of Poitiers, where he earned his diploma in the French language the following year. From 1963 to 1965, Slusser served in Germany assigned to US Army intelligence. In 1965 Slusser married French academic Danièle Chatelain, to whom he would remain married for life. Slusser attended Harvard University, afterward taking a Fulbright Fellowship in Germany as well as serving as a Harvard traveling fellow in France. From 1971 to 1975 he taught English at California State College at San Bernardino as an assistant professor, also working as a freelance author, critic, and translator throughout this period. Although Slusser had been a fan of science fiction as a teen his interest in the genre was reignited in San Bernardino. In 1976 Slusser returned to France as a Fulbright lecturer at University of Paris.