Leggett focused on fish ecology and graduated in 1965, and at Power's advice, began his PhD at McGill University in zoology, completing in 1969.

[10][13] He eventually became a full professor in 1979, the Chair of the Department of Biology in 1981, the Dean of Science in 1986, and lastly the Vice-Principal of Academics in 1991.

[7] In October 1993, Queen's University announced the appointment of Leggett as the 17th Principal and Vice-Chancellor, succeeding David Chadwick Smith.

[23] He also oversaw the opening of the expanded Agnes Etherington Art Centre building in 2000,[25][26][27] the opening of the Cancer Research Institute Complex[28] and the new Leonard Hall cafeteria in 2003,[29] and the renovation of Gordon Hall (the old building for the Department of Chemistry),[30][31] including the demolition of the Frost Wing,[32][33][34] throughout his second term of Principalship.

[46][47] Leggett, however, continued to advocate for deregulation, outlining his idea in the Pathfinder Proposal submitted to the Ontario government in 2002,[48][49] and sending representatives to meet with Harris.

[51][52][53][54] Leggett was unhappy with the province's decision,[55] and announced significant reduction to Queen's budget and that the replacement of teaching staff would be limited to loss by retirement.