Dennis R. Mock began teaching courses in Geography as a professor in the Social Sciences Department at Ryerson in 1971. By 1974, Mock was a permanent Ryerson Faculty member. From 1979 to 1987, he acted at the Chair of the Department of Geography and helped establish the School of Applied Geography -- the first applied geography program in Canada. In 1987, Mock was awarded the Distinguished Service Award of the Canadian Association of Geographers for his role in helping restructure the Ontario high school geography curriculum. In 1988, Mock was appointed Registrar.
Mock served on numerous Ryerson executive committees over the course of his career. He was appointed VP Academic in 1989, a post he held until 2000. From August 1990 to January 1991, Mock fulfilled the role of Acting President while then-President was on sick leave. In 1999, Ryerson University established the Dennis Mock Student Leadership Awards, granted to students in recognition of "extra-curricular contributions to the life of the Univeristy" (eForum, April 14, 2000). Mock retired from Ryerson in 2000. From 2003 to 2009, Mock served as the fourth President and Vice-Chancellor of Nipissing University after a one-year term as Interim President.