A native of Putnam, Connecticut, Wilcox graduated from Wesleyan University in 1961 and later received a doctorate in history from Harvard in 1967. Wilcox was at the University of Chicago's Newberry Library conducting research when he first met John Bellairs. He later moved to Boston, where Bellairs caught up with him when he returned from England in 1968.
Wilcox joined the faculty at the University of New Hampshire in 1970, regularly instructing courses on the Renaissance and Reformation and European Intellectual History. Friends and colleagues described Wilcox as a "brilliant historian" and a "clear and acute analyst with an astonishing breadth of vision" whose courses were particularly sought by graduate students because of his thorough knowledge of the material at hand. Later he was the history department's director of graduate studies (1973-79) and department chairman (1982-85). Earlier, he was a member of the Harvard University faculty.
He authored three books:
- The Development of Florentine Humanist Historiography in the Fifteenth Century (1969), a reworking of his doctoral thesis. Shortly after his research many of the primary sources were lost in the November 1966 Arno River flooding of Florence, thereby making his book the definitive work.
- In Search of God and Self: Renaissance and Reformation Thought (1975)
- The Measure of Times Past: Pre-Newtonian Chronologies and the Rhetoric of Relative Time (1987)
- The pedantic tendencies of Snodrog were inspired by Wilcox: "[Don] was not...obnoxious, nor [were] his brain cells winked out...[but] he was an erudite academic nitpicker."
- Wilcox's connection to the University of New Hampshire is shared through Bellairs's character of Professor Charles Coote, both historians. Coote is described at one point as being a "pedant" and wearing horn-rimmed glasses (The Bell, the Book, and the Spellbinder, 98).,