After retiring, she served as president of both the Maryland and Baltimore City League of Women Voters, and campaigned successfully for single representation of 14 City Council districts.
"Whether it was at work serving seniors and families at the Social Security Administration or her years advocating for more women in public service, Millie demonstrated a deep commitment to social justice," said Maryland Sen. Barbara A. Mikulski.
"Families across Maryland and our nation have been better served because of Millie's steadfast dedication to service, community and neighbor helping neighbor. Millie was a strong supporter of women's rights, particularly in the area of financial security. She was a great friend and a wonderful adviser."
Born Mildred Marie Lund on a farm near Cedar Falls, Iowa, she earned a bachelor's degree in history from Iowa State Teachers College and then taught high school. When she was a graduate student in Iowa, a professor recommended her for an opening at the Social Security Administration in Baltimore.
She moved to Baltimore in 1943 as a temporary wartime worker for Social Security and completed her master's degree in public administration while living in a Eutaw Place rooming house.
"Eleanor Roosevelt was a pivotal influence in Millie's life and worldview. Millie had the privilege of meeting her in the summer of 1942 while taking a course at American University," said her son, Joseph Tyssowski Jr. of Glenwood. "My mother grew up in the Depression, and the first lady was her idol."
She met a fellow Social Security worker, Joseph Tyssowski Sr., and they married in 1947. She moved with him as he took other assignments within the agency.
In an oral history, she recalled taking a pay cut to work as a lower-grade clerk when her husband was transferred to San Francisco.
"This experience ... was really invaluable in my later experience as a budget officer because I got the feeling of operations and understanding of the workings at the public level of the Social Security program," she said.
"She was good at dealing with people. She was assertive but also caring," said her son. "She was a hard worker and a good manager. At the end of the day, she would fall asleep in a chair with work she had brought home still in her lap."
Mrs. Tyssowski became Social Security's top budgeting officer and often appeared before congressional committees to defend administrative costs.
She retired in 1980 as the director of Medicare operations in the Health Care Financing Administration.
An Evening Sun article published at the time of her retirement called her one of the highest-ranking female federal executives in the Baltimore area. She received distinguished service awards from the Department of Health, Education and Welfare and the Federal Government Accounting Association.
After retirement Mrs. Tyssowski became an active volunteer. She joined the League of Women Voters and the Friends of the Enoch Pratt Free Library.
In 2006, she was quoted in The Baltimore Sun when a court ordered the Baltimore Development Corp. to reveal more of its activities.
"People are suspicious of government agencies that operate in the dark," she said. "I think there is greater confidence if they operate in the sunshine."
In addition to her work with the state and Baltimore City League of Women Voters organizations, she was active in the lobbying corps of the National League of Women Voters.
"She was a leader and understood the processes of getting things organized and publicized," said the Baltimore League's co-president, Lois Hybl. "She could bring people together."
Mrs. Tyssowski took classes at the Osher Lifelong Learning Institute at the Johns Hopkins University.
In 1988, Mayor Kurt L. Schmoke named her to the Baltimore City Commission for Women. Family members said she helped female entrepreneurs and furthered the participation of women in business and government. While on the commission, she helped organize the nonprofit Women Entrepreneurs of Baltimore to assist low-income and disadvantaged women gain self-sufficiency through training.
She lived in Catonsville and later bought a historic home in Dickeyville, where she gardened and worked with its community association.
"You would see her striding about the village," said WBAL-TV news anchor Donna Hamilton, a friend. "She was an amazing and active woman. She was admired by so many people."
Mrs. Tyssowski enjoyed the arts. She attended performances at Center Stage, Everyman Theatre and the Baltimore Symphony Orchestra. In 1985, she was the co-founder and charter president of the Women Composers Orchestra, a chamber orchestra-sized group made up of men and women dedicated to performing only music by female composers. It performed until 1995.
Mrs. Tyssowski also traveled with the World Affairs Council of Philadelphia. Family members said that on her visits to Russia, Egypt, the Netherlands, China, Turkey, Ireland and Cuba, she was interested in those country's cultures, governments, and education and health systems.
A life celebration will be held from 4 p.m. to 9 p.m. Saturday at 2500 Pickwick Road.
In addition to her son, survivors include a daughter, Judy Marie Wheatley of Nashville, Tenn.; seven grandchildren; and three great-grandchildren. Her husband of 33 years died in 1981. A son, John Edwin Tyssowski, died in 2012.