Walsh supported the passage an ordinance in the city council which regulated short-term rental of housing units, which he signed into law in 2018.

[5] When Walsh initially announced his candidacy, he lacked substantial name recognition outside of his own state house district.

"[8] David Scharfenberg of WBUR considered Walsh's candidacy as being, "built on his against-the-odds biography: a son of Irish immigrants who overcame a childhood fight against cancer and a young adult's struggle with alcoholism.

[9] As a result, he advanced to the general election, facing second place vote-getter Boston City Councilor John R. Connolly, who received 17.2% of the vote.

[12] Ryan also credited the general election endorsements of eliminated mayoral candidates John Barros, Felix G. Arroyo, and Charlotte Golar Richie as helping Walsh to overcome Connolly's initial polling lead.

He advanced to the general election and faced second place vote-getter, Boston City Councilor Tito Jackson, who had received 29% of the vote.

[22] In December 2019, Milton J. Valencia of The Boston Globe opined that, beginning under the City Council presidencies of Michelle Wu (in 2016 and 2017) and Andrea Campbell (beginning in 2018), the council had "been, perhaps, the most aggressive in recent history in pushing reforms, often to the left of the mayor, on issues addressing climate change and economic and racial equity.

[32][33] Walsh was seen as friendly towards real estate developers throughout his mayoralty, and Boston underwent a substantial building boom during his seven years in office.

[34] During the course of his mayoralty, officials in Boston granted approval to 7.7 million square feet of real estate developments, including more than 40,000 more housing units.

[35] Steve LeBlanc of The Associated Press wrote in 2021, "during his tenure as mayor, Walsh has overseen the city's ongoing rejuvenation, which has led to challenges that include gentrification and rising housing costs.

[43] Similarly, Bill Forry of the Dorchester Reporter wrote that, prior to the outbreak of the COVID-19 pandemic, Walsh's tenure was characterized by, "remarkable growth and relative peace and prosperity.

[3] In March 2015, Walsh and Councilor Michelle Wu co-authored an op-ed in The Boston Globe calling paid parental leave, "a must for working families".

[54] The planned race faced opposition, including from residents of nearby neighborhoods who expressed concerns over impacts such as noise and additional traffic.

The president of the Grand Prix of Boston's corporate board blamed the cancellation on demands made by Walsh's mayoral administration, which he characterized as unreasonable.

[64][65] However, in December 2017, Walsh signed into law a plastic bag ban authored by City Councilors Michelle Wu and Matt O'Malley.

[67] Later that year, he unveiled plans to renovate a facility to house hundreds of homeless people displaced due to the closure of the Long Island Bridge.

[77] In January 2021, upon Gross' retirement, Walsh made Dennis White, also African American, the new commissioner of the Boston Police Department.

[97][98] The racial equity fund launched months later,[99] with Walsh stating it would invest in nonprofits that, "empower Black and brown residents in economic development, in public health, in youth employment, in education, in the arts, and other areas.

[101] In 2014, Walsh refused to march in the city's Saint Patrick's Day parade due to LGBTQ groups being blocked from participating.

[110][111] At a joint forum with Governor Baker in February 2018, Walsh expressed skepticism towards safe injection sites as a means of dealing with the impacts of the opioid epidemic, remarking, "I just don't see how that helps.

[117] Walsh urged Bostonians to adhere to social distancing guidelines, and made efforts to limit public activity.

[115] Days after declaring a state of emergency, he suspended all construction projects and closing all of the Boston Public Library locations and city community centers.

[115][121][122][123] On March 16, 2020, Walsh announced the Boston Resiliency Fund, a city-led fundraising effort to support programs and charities serving those impacted by the pandemic.

Walsh justified his rejection of Shurtleff's petition with a First Amendment rationale tied to the government speech doctrine and the Establishment Clause of the First Amendment, arguing that permitting the flying of this "Christian Flag" would be perceived as a city government endorsement of Christianity over other religions in violation of the Establishment Clause.

In the unanimous Shurtleff v. City of Boston decision, the Supreme Court of the United States rejected that the matter amounted to government speech, and therefore found that the Boston city government's actions were in violation of Shurtleff's rights under the First Amendment's Free Speech Clause by performing viewpoint discrimination.

To reach this ruling, the court weighed the circumstances of the situation, including what it found to be a lack of meaningful involvement by the city government in selecting flags previously flown.

[151] Walsh worked with Councilor Ayanna Pressley on an ordinance requiring municipal trucks to have side-guards in order to protect cyclists.

[154] He dropped his legal objections in January 2016, after striking a deal between the city of Boston and Wynn Resorts, who were behind the Everett casino project.

[163][164] The city-commissioned study also found that, between July 1, 2014, and June 30, 2019, only 1.2% of the $2.2 billion that Boston spent on contracts and procurement went to Black-owned or Latino-owned businesses.

[165] In February 2021, Walsh signed an executive order making it a stated goal for 25% of city contracts to be awarded to businesses owned by minorities or women.