He went on to graduate studies in mathematics at Harvard University, earning a master's degree in 1972 and a doctorate in 1978.

After leaving Harvard, he worked at Bell Labs for four years before joining the Albany faculty in 1983.

[5] Although trained as a mathematician and employed as a computer scientist, Willard's most highly cited publication is in evolutionary biology.

[7] Willard's 1978 thesis work on range searching data structures[paper 2] was one of the predecessors to the technique of fractional cascading,[8] and throughout the 1980s Willard continued to work on related data structure problems.

As well as continuing to work on range searching, he did important early work on the order-maintenance problem,[paper 3] and invented the x-fast trie and y-fast trie, data structures for storing and searching sets of small integers with low memory requirements.

[paper 4] In computer science, Willard is best known for his work with Michael Fredman in the early 1990s on integer sorting and related data structures.

In research originally announced in 1990, Fredman and Willard changed these assumptions by introducing the transdichotomous model of computation.

[paper 5][9] In a follow-up to this work, Fredman and Willard also showed that similar speedups could be applied to other standard algorithmic problems including minimum spanning trees and shortest paths.

[paper 7] In a preprint summarizing his oeuvre of work in this area, Willard speculated that these logical systems will be of importance in developing artificial intelligences that can survive the potential extinction of mankind, reason consistently, and recognize their own consistency.