Malloy began his career as an assistant district attorney in New York in 1980 before moving back to Stamford and entering private practice.

[1][2] Rell did not run for reelection, and Malloy faced former United States Ambassador to Ireland Thomas C. Foley in the general election, defeating him by fewer than 6,500 votes.

[15] Malloy made crime reduction a priority during his tenure as mayor; Stamford saw a dramatic decrease in homicides under his administration.

On February 3, 2009, Malloy officially filed paperwork with Connecticut's State Elections Enforcement Commission to form a gubernatorial exploratory committee,[19] and subsequently announced that he did not intend to seek re-election as Mayor of Stamford.

Malloy faced Republican Thomas C. Foley, the former United States Ambassador to Ireland under President George W. Bush, in the race for governor.

[25] According to The New York Times on November 3, Malloy was elected governor; they later placed Foley in the lead with no declared winner.

[27] Foley's team looked into the events that took place in Bridgeport and determined there was insufficient evidence of enough fraud to overcome the vote deficit.

On August 12, Tom Foley, Malloy's Republican opponent in 2010, won his party's nomination,[30] making the 2014 election a rematch of the bitter 2010 contest.

[37] The first task facing Malloy upon taking office was addressing a multibillion-dollar deficit as a result of the prior state budget enacted by the Democratic super-majority-controlled legislature which Rell chose to accept without signing.

[55] Disability advocates objected to being excluded from the decision-making process, to union interference in the intimate relationship between employers and PCAs, and to the likely loss of PCA hours under a capped program; NFIB feared a "terrible precedent" in allowing other union organizing drives of small businesses by executive order through card check; and legislators viewed Malloy's actions as a violation of the state Constitution's separation of powers.

Malloy responded that these workers, whom he described as being among the hardest working and lowest paid, deserved the opportunity to collectively bargain if they wished to do so.

Malloy, who has long campaigned against capital punishment,[56] signed a bill to repeal the state's death penalty on April 25, 2012.

[57][58] On August 13, 2015, however, the Connecticut Supreme Court ruled in 2015 in State v. Santiago that the legislature's decision to prospectively abolish capital punishment rendered it an offense to "evolving standards of decency," thus commuting the sentences of the 11 men remaining on death row to life in prison without parole.

[59] Malloy was in the process of having Connecticut be the first state in the nation to raise the age of being within the juvenile system from 18 to 21 via the Second Chance initiative.

[60][needs update] Malloy's "centerpiece" education reform bill was unanimously passed by the Connecticut House of Representatives and signed into law in early May 2012.

[61] Also in May 2012, Malloy signed a bill that expanded voting rights in Connecticut, allowing for same-day voter registration.

[63] In the wake of the Sandy Hook Elementary School shooting in Newtown in December 2012, Malloy pushed for strict new gun control laws.

In April 2013, he signed into law a bill that passed the legislature with bipartisan support and required universal background checks, banned magazines with a capacity of more than 10 rounds, created the country's first registry for dangerous-weapon offenders and added over 100 types of gun to the state's assault weapons ban.

[64] In December 2015, Malloy announced he would issue an executive order to prohibit anyone on federal terrorist watchlists (such as the No Fly List) from obtaining the permits required to acquire firearms in Connecticut.

[66] On June 7, 2013, Malloy signed a bill that allows all residents of Connecticut, including illegal immigrants, to apply for a driver's license.

Connecticut, Georgia, Indiana and Minnesota had previously been the only states that still had broad restrictions on the sale of alcohol on Sundays.

[70] On October 28, President Barack Obama approved Connecticut's request for an emergency declaration, and hundreds of National Guard personnel were deployed.

[73] Malloy's strong initial response is credited with helping the state to avoid much of the damage that affected neighbouring New York City and nearby New Jersey.

[74] Malloy was unanimously chosen by the University of Maine System Board of Trustees to be its Chancellor on May 30, 2019, with his service beginning on July 1.

[82] In 2007, Malloy's youngest son, Sam, then 14 years old, was involved in an incident in which he and a group of other boys at Stamford High School allegedly called Candace Owens and left racist hate speech and violent threats on her voicemail.