Fitzgerald was born in Boston, the son of Irish immigrants. He became a banker in Boston and was active in the local Democratic Party. In 1892 he became a member of the Massachusetts Senate and would later be elected to Congress. In 1906 Fitzgerald became the mayor of Boston. He was the most prominent political figure in the city of Boston along with Patrick J. Kennedy.
In 1914 these two powerful political dynasties (Kennedy and Fitzgerald) were united when Joseph P. Kennedy, Sr married Fitzgerald's daughter Rose.
Fitzgerald was an unsuccessful candidate for Governor of Massachusetts in 1922.