The former Speaker of the Massachusetts House of Representatives originally joined the state legislature in 1979, as a member of the Democratic Party.

DiMasi is the third consecutive Massachusetts house speaker to later become a convicted felon due to crimes committed in office.

In April 2006, Governor Mitt Romney signed the first-in-the-nation universal health insurance bill into law.

As a result of the law, Massachusetts reduced the number of uninsured adults by nearly half within the first year of mandatory health coverage and increased the percentage of people receiving routine preventive care, according to the first major study of the 2006 law conducted by the Urban Institute.

[3][4] In 2007, Massachusetts governor Deval Patrick submitted a bill that would allow the construction and operation of three resort-style casinos in the state.

[5][6] Patrick's proposed that the revenue generated would be spent to beef up local law enforcement, create a state gambling regulatory agency, repair roads and bridges ($200 million), gambling addiction treatment ($50 million) and the remainder would go towards property tax relief.

[12][13][14] According to The Boston Globe, "DiMasi and three of his close friends and associates are the subjects of the Ethics Commission probe and other investigations relating to large payments the associates received from Cognos ULC ..." an IBM owned company based in Ottawa, Ontario, Canada, with a United States headquarters in Burlington, Massachusetts.

The Globe also said that "One of the associates, Richard Vitale, DiMasi's accountant, also accepted payments from ticket brokers who were seeking to gut state antiscalping laws."

[16] His resignation made DiMasi the third straight Speaker of the Massachusetts House of Representatives to leave office under a legal or ethical cloud.

[23] On September 9, 2011, DiMasi was sentenced to eight years in federal prison by U.S. District Court Judge Mark Lawrence Wolf and ordered to pay a fine of $65,000.

[29] In November 2016, Judge Mark L. Wolf released a 69-page ruling concluding that DiMasi, US Attorney Ortiz’s office, and federal prison officials convincingly demonstrated that DiMasi's health has declined so severely that further imprisonment was no longer warranted due to a severe illness.

[32] On April 22, 2019, the state of Massachusetts rejected DiMasi’s application to lobby the legislature and later in the week, he registered as a lobbyist with the city of Boston.