Gerrard became active with the Liberal Party of Canada while working on his undergraduate degree, impressed with Prime Minister Lester Pearson's positions on social and international issues. He was a delegate to the Liberal Party's 1968 leadership convention, supporting John Turner. He later volunteered for the "Non" side in the 1980 Quebec referendum, and became Liberal riding president for Lisgar in 1984. In 1990, he was Manitoba co-chair of Jean Chrétien's successful bid for the Liberal Party leadership.