Chang-Díaz was educated at the University of Virginia. She entered politics while serving as a legislature aide for Massachusetts Senator Cheryl Jacques and as a campaign manager for MassEquality. She attempted to win election to the state senate in the 2006 election as a write-in candidate in the Democratic primary, but lost to incumbent Senator Dianne Wilkerson, who was also running as a write-in candidate. She ran again in the 2008 election and defeated Wilkerson in the primary and general elections.
Massachusetts Senator Dianne Wilkerson failed to file her nomination petition with enough valid signatures to appear on the ballot in the Democratic primary during the 2006 election, but announced that she would run a write-in campaign for the Democratic nomination.[6] Chang-Díaz announced on June 18, 2006, that she would run as a write-in candidate in the primary.[5] Wilkerson defeated Chang-Díaz in the initial primary, but a judge ordered a recount due to write-in votes not being counted in eight precincts.[7] Secretary of State William F. Galvin started an investigation into Boston's handling of elections due to the error.[8] Chang-Díaz turned in enough signatures for a recount of all ten wards.[9] The final recount determined that Wilkerson had won by 767 votes which was more than the initial 141 votes.[10] Wilkerson won reelection in the general election.[11]
Chang-Díaz with supporters at her November 2008 election night celebration
Chang-Díaz ran against Wilkerson in the 2008 Democratic primary and defeated Wilkerson.[12][13] A recount was conducted and maintained Chang-Díaz's victory.[14] Wilkerson launched a write-in campaign in the general election, but withdrew after she was arrested on charges of public corruption and Chang-Díaz defeated Wilkerson and independent candidate William Theodore Leonard in the general election.[15][16][17] She was the first Hispanic woman elected to the Massachusetts Senate.[18]
She won reelection without opposition in the 2010, 2012, 2016, 2018, and 2020 elections.[19][20][21][22][23] She defeated Republican nominee David James Wyatt in the 2014 election.[24]
Chang-Díaz announced on June 23, 2021, that she would seek the Democratic nomination in the 2022 gubernatorial election, but ended her campaign on June 23, 2022, although she remained on the ballot.[33][34]
Chang-Díaz was critical of legislation passed by the Massachusetts Senate which targeted the ability of undocumented immigrants to obtain services from the state including Medicaid and public housing.[35] She opposed casinos stating that they were "a fancy way of putting a tax on the poor."[36] Chang-Díaz supported raising the income tax to increase education funding.[37]
She sponsored legislation to include transgender people in Massachusetts's anti-discrimination laws in 2011.[38] She supported legislation which allowed people to use gendered-public places that matched their gender identity and gave protections against discrimination for transgender people.[39]
