Born in Missouri, Shaheen received a bachelor's degree in English from Shippensburg University and a master's degree from the University of Mississippi. She taught high school in Mississippi and moved to New Hampshire in 1973, where she taught school and owned a small business. A Democrat, she worked on several campaigns before running for office in 1990, when she was elected to the state Senate. In 1996 she became governor. She served three terms before stepping down to run for the U.S. Senate. She was defeated by Republican John E. Sununu.
She and her husband, Bill, have three children.