Susan Armitage received a bachelor's degree in philosophy from Wellesley College in 1959, a master's degree in American history from San Jose State College in 1965, and earned a Ph.D. at the University of London in 1968. From 1973 to 1978 she served as a visiting assistant professor of history at the University of Colorado where she directed the Boulder Women's Oral History Project.

Armitage joined the faculty at Washington State University in 1978 as the first director of Women's Studies and as an Assistant Professor in History. She served as director of the WSU American Studies program, as editor of Frontiers, a nationally recognized feminist journal, and as the director of the Center for Columbia River History. She retired in 2008. During her thirty years of service she distinguished herself as a teacher, administrator, graduate student advisor, and as a research scholar.

Armitage was one of the first scholars to examine the role of women in the American West through teaching, research, articles, books, and service. She developed and taught the first two undergraduate U.S. Women's history courses at WSU. She co-edited The Women's West (1987) and Writing the Range (1997). Additionally, she was the only non-Ivy League member author of the U.S. history text book Out of Many (2000), in which she was able to incorporate social history and the crucial activities of women into the standard political narrative of U.S. history. In 1991, Armitage was recruited by Toni Dewey, founder of the Women of the West Museum in Boulder, CO, to serve as trustee and academic expert in charge of research and development of the storyline and exhibit planning. She worked with the museum until 1997 to create a multicultural storyline, an idea that was new and challenging at the time.

Throughout her tenure at WSU, Armitage was a key strategist in long-term efforts to advance women, promote the preservation of women's history, and encourage diversity at the university. She contributed greatly to the Washington Women's Heritage project, the Oral History Office, the Association for Faculty Women, the Commission on the Status of Women, the President's Commission of the Status of Minorities, and Diversity Design Committee.

During the course of her career Armitage also shared her commitment to women's history and American Studies with students, colleagues, and others outside the United States. In 1990, she spent two weeks in Vladivostok, Soviet Union, as a member of a WSU delegation sent to inaugurate an exchange agreement with Far Eastern University. In 1993, she traveled to India for two weeks as a lecturer sponsored by the United States Information Agency (USIA). She lived and lectured in Moscow, Russia from February to June 1995 as the Distinguished Fulbright Chair in American History at Moscow State University. She also spent to two weeks lecturing in Azerbaijan and Estonia and Belarus, again representing USIA.

Armitage was named a Mellon Scholar at the Wellesley College Center for Research on Women (1984) and a Hilliard Scholar at the University of Nevada at Reno (1990). In 2003-2004, she was a Senior Fellow at the Beineke Library and the Lamar Center for the Study of Frontiers and Borders at Yale University. She served on the editorial boards of the Western Historical Quarterly, for the Women in the West Series, the Journal of the West, the Oral History Review, and Pacific Northwest Quarterly. She was appointed to the Governor's Advisory Council on Historic Preservation, and as acted as a consultant for Northern Nevada Community College on integrating women into the curriculum. Her work led to her being invited to the White House by Laura Bush in 2003, and, in 2008, she was named Washington State University Woman of the Year.