Moser's Ph.D. Thesis, written at the University of Toronto under H. S. M. Coxeter, evolved into the oft-cited standard Ergebnisse reference on combinatorial group theory (1957) known to generations as "Coxeter and Moser." Before arriving at McGill he held faculty positions at the University of Saskatchewan and the University of Manitoba. Much of his later seminal mathematical work was in discrete geometry, where, with Peter Brass and Janos Pach, he published in 2005 Research Problems in Discrete Geometry. Moser's interest in problem solving extended far beyond this definitive monograph, and he was active for many years in provincial and national mathematics competitions for pre-university students, and in the publication for the Mathematical Association of America of Five Hundred Mathematical Challenges with E. Barbeau and M. Klamkin; with bawdy humour and other irreverence, problem solving was but one of the missions he shared with his older brother Leo Moser (1921-1970), who was also a mathematician.
Willy served as President (1973- 1975) and in other capacities in the Canadian Mathematical Congress -- the predecessor to the Canadian Mathematical Society, and received their Distinguished Service Award in 2003. His experience in editing the Congress's journals served him well subsequently in multiple capacities, including editing his friends' writing -- whether or not they requested it. Moser's relations with colleagues were more brotherly than collegial. Typically one might find in his entourage a speed chess match, a peripatetic friend expounding latest discoveries and conjectures, and others enjoying the conversion to mathematics of the potent coffee Willy brewed for his academic family, all bathed in the pungent second-hand smoke of Willy's cigar or pipe. He stubbornly remained active as an Emeritus Professor at McGill after his retirement in 1997, and after a subsequent, debilitating stroke. On receiving the CMS Distinguished Service Award in 2003, he addressed the audience in these terms:
Be generous and patient as teachers, be active in projects which benefit the mathematical community and, above all, have as long and as happy a mathematical life as I have had, and am still having.