An Irish-American of Catholic background, Hicks was elected to the Boston School Committee in 1961. In January 1963, she became chairperson and seemed likely to be endorsed by the leading reform group, when, in June, the Boston chapter of the NAACP demanded "an immediate public acknowledgment of... segregation in the Boston public school system".
At the time, thirteen city schools were at least 90% black — but the Committee refused to acknowledge the segregation. Hicks was recognized as the holdout, and within months she became Boston's most popular politician, but also the most controversial, requiring police bodyguards 24 hours a day.
Hicks became nationally known in 1965 when she opposed court-ordered busing of students into inner-city schools to achieve integration. By refusing to admit segregation existed in city schools, and by declaring that children were the "pawns" of racial politics, for many she symbolized hatred of blacks among Boston's Irish-Catholic working class. According to Hicks: "Boston schools are a scapegoat for those who have failed to solve the housing, economic, and social problems of the black citizen."
In 1967, she came within 12,000 votes of being elected mayor of Boston. Hicks later served one term in the US House of Representatives from 1970 to 1972.
Hicks was conservative in racial matters but progressive in other ways. She was a member of the National Organization for Women, and while in Congress she lobbied for passage of the Equal Rights Amendment. In 1976, she was elected the first woman president of the Boston City Council.