[6] Martin's father served as a bombardier in the U.S. Army Air Force in the Pacific theater during the Second World War, and recalled witnessing the mushroom cloud rise over Hiroshima while on a routine mission.

[13] In 1986, while in law school, O'Malley was named by then-Congresswoman Barbara Mikulski as state field director for her successful primary and general election campaigns for the U.S. Senate.

He's considered something of a loose cannon at City Council meetings, where the sight of him rising from his chair and clearing his through causes half the room to lean forward in anticipation[19]O'Malley announced his decision to run for Mayor of Baltimore in 1999, after incumbent Kurt Schmoke decided not to seek re-election to a third term.

[25] His strongest opponents in the crowded Democratic primary of seven were former City Councilman Carl Stokes, Baltimore Registrar of Wills Mary Conaway, and Council President Lawrence Bell.

[26] In his campaign, O'Malley focused on reducing crime and received the endorsement of several key African-American lawmakers and church leaders, as well as that of former mayor of Baltimore and Maryland governor William Donald Schaefer, who had served from 1971 to 1987.

[27] On September 14, he won the Democratic primary with a 53% majority[28] and went on to win the general election with 90% of the vote, defeating Republican Party nominee, developer David Tufaro.

In his first year in office, he adopted a statistics-based tracking system called "CitiStat", modeled after Compstat, a crime-management program first employed in the mid-1990s in New York City.

The Washington Post wrote in 2006 that Baltimore's "homicide rate remains stubbornly high and its public school test scores disappointingly low.

O'Malley has been accused by many of establishing a zero-tolerance policing strategy, aimed at reducing the city's high murder rate but that instead led to the targeting and abuse of black communities.

The Washington Post wrote at the time that "no evidence has surfaced of a systemic manipulation of crime statistics," but that "there is no quick or definitive way for O'Malley to prove his numbers are right.

This bid was considered a long-shot, as the city lacked a standard venue of sufficient space and capacity to host a major party presidential nominating convention.

Baltimore's bid proposed the unusual solution of erecting a temporary canopy at Oriole Park at Camden Yards in order to provide a venue.

[55] Major land developer Edward St. John was fined $55,000 by the Maryland Office of the State Prosecutor for making illegal contributions to the 2006 O'Malley gubernatorial campaign.

[60] In April 2009, he signed the traffic speed camera enforcement law he had supported and fought for to help raise revenue to try to overcome an imminent state deficit.

[69] The law provides that undocumented immigrants can be eligible for in-state tuition if they have attended a high school in Maryland for three years, and if they or their parents have paid state income taxes during that time.

[72] During the 2014 crisis involving undocumented immigrant children from Central America crossing the border, O'Malley refused to open a facility in Westminster, Maryland, to house them.

"As advocates for the truths we are compelled to uphold, we speak with equal intensity and urgency in opposition to your promoting a goal that so deeply conflicts with your faith, not to mention the best interests of our society.

The signature of this bill made Maryland the first East Coast state to make it illegal to possess, sell, trade or distribute shark fins.

He had previously blocked the technique from the region for three years, awaiting the report from the Marcellus Shale Advisory Commission on the risks and benefits of this controversial procedure.

[104] After months of consideration, O'Malley indicated on Twitter that he would announce his candidacy on May 30, 2015, at Baltimore's historic Federal Hill Park, overlooking the city's picturesque downtown skyline and the Inner Harbor.

So as we march forward to the fall, let us all resolve together that the love, the generosity, the compassion and the commitment of this campaign will continue to point our country forward.Four months later, on June 9, 2016, O'Malley officially endorsed Hillary Clinton.

[107] After the end of his presidential campaign, there was speculation that O'Malley was a possible choice for United States Secretary of Homeland Security, should Hillary Clinton be elected president.

[109] On May 5, 2016, O'Malley joined the MetroLab Network, a group focusing on city–university partnerships and based at Heinz College (the public policy school of Carnegie Mellon University) in Pittsburgh, Pennsylvania.

[112] The Baltimore Sun reported on May 31, 2017, that O'Malley admitted that he along with other Democrats gerrymandered the state's 6th district in a successful effort to oust long-time Republican incumbent Rep. Roscoe Bartlett in 2012.

"[113] In November 2019, O'Malley encountered acting deputy secretary of the Department of Homeland Security, Ken Cuccinelli II, in a Capitol Hill bar and confronted him with what The Washington Post reported one witness described as a "shame-invoking tirade" centering on the Trump administration's immigration policies.

[123] O'Malley analyzed data to find that the two greatest contributors to the length of processing times for claims were in state agency reviews and Social Security Agency-run hearings.

In response to these findings, O'Malley has pursued having the workload of handling claims be more flexibly shared, and has also sought greater engagement with external advocacy groups.

"[123] O'Malley resigned from the Social Security Administration on November 29, 2024, in order to launch his candidacy in the February 2025 election of a new Democratic National Committee chairperson.

[134] While attending Gonzaga College High School in Washington D.C. in 1979, O'Malley and his football coach Danny Costello formed a band, Shannon Tide, which played Irish music and folk rock.

In 2012, it played at the White House for 44th President Barack Obama as part of an extended Saint Patrick's Day celebration honoring Irish Prime Minister Enda Kenny.