Dennett did not become active in the women's suffrage movement until her marriage began to break up. Later, she wrote, "I went into suffrage work, as perhaps you know, because I needed an anaesthetic at the time, and suffrage was the nearest thing at hand that was unconnected with my previous work." Dennett began her work as field secretary of the Massachusetts Suffrage Association, organizing lectures, rallies, sermons, cheap meals, speaking tours to gather signatures for petitions, and similar outreach efforts. Dennett's opinion on why women deserved the vote was simple: "Our basic principles that 'governments derive their just powers from the consent of the governed' [...] undeniably imply the right of women to direct representation by the vote, since women are governed and women are people."