Before entering public life, Wagner worked as an English and math teacher, and operated her own successful publishing business. She began her political career on the Staten Island Community School Board, which she chaired. She went on to serve on the New York City Board of Education, and was its vice president from 1978 to 1979.
In 1981, Wagner was elected to the New York City Board of Estimate as the representative of Staten Island. She was the only woman on the board, and served until its abolition in 1989. During her time on the board, she was a strong advocate for Staten Island, and was instrumental in securing funding for many important projects, including the Staten Island ferry terminal, the Staten Island Expressway, and the College of Staten Island.
In 1991, Wagner was elected as president of the New York City Council. She was the first woman to hold this position. During her tenure as president, she was a strong advocate for education, and worked to increase funding for public schools. She also supported initiatives to improve the city's economy and infrastructure.
After her time in public life, Wagner continued to be active in the community. She served on the boards of several nonprofit organizations, and was a vocal advocate for women's rights. She also worked as a consultant and public speaker.
Wagner died of complications from heart surgery on December 15, 2011, at the Staten Island University Hospital in Ocean Breeze, Staten Island, New York City, at the age of 78, one day before her 79th birthday. She was survived by her husband, Robert, her four children, and her ten grandchildren.
Wagner was a trailblazer for women in politics, and her contributions to Staten Island and New York City were significant. She was a strong advocate for her community, and her work helped to improve the lives of many people.