He served as a legislative affairs specialist at the United States Department of Labor for five years during the Clinton administration, working on matters related to expanding access to affordable healthcare and efforts to increase federal minimum wage.

In 2007, Flynn unsuccessfully ran in a special election for the 2nd district seat on the Boston City Council, placing third in the nonpartisan primary.

[3] Flynn graduated from Boston's Don Bosco Technical High School and from Newport, Rhode Island's Salve Regina College, where he studied history and government.

[3] He served active duty at Joint Task Force Guantanamo, and had further service abroad in the United States Naval Reserves.

[3] At the Department of Labor he worked on matters related to expanding access to affordable healthcare and efforts to increase the federal minimum wage.

[9] In 2007, Flynn ran in the second district special election to fill the seat left vacant by the death in office of James M. Kelly.

[6] In December 2018, the Boston City Council unanimously voted to pass an ordinance that Flynn authored with Lydia Edwards that extended the period of repayment for back taxes by low-income elder residents, and forgave interest.

"[19] In late-2019, Flynn partnered with Councilwomen Wu and Edwards to hold a hearing meant to identify possible loopholes in the enforcement of the short-term rental regulation ordinance adopted the previous year.

[4] In the early weeks of the COVID-19 pandemic impacting the United States, Flynn introduced a resolution to express the council's support towards the city's Chinese and broader Asian communities.

[24] In 2021, Flynn voted against legislation that was passed by the City Council which restricted the use of rubber bullets, tear gas, and pepper spray by the Boston Police Department.

The campaign process for those seeking the presidency typically occurs behind closed doors, with the contenders privately lobbying and negotiating with members of the council for their votes.

[6] During his third council term, Flynn was joined councilors Frank Baker, Michael F. Flaherty, and Erin Murphy in an informal grouping that often functioned as a centrist voting bloc.

[31] However, during his tenure as council president, Flynn personally stated that he had a good working relationship with Wu and that he saw it as important to collaborate with her mayoral administration.

[42] After Wu left, Flynn text messaged a statement to the Boston Herald in which he declared, As acting mayor and city council president, I will continue to work closely with Mayor Wu and our colleagues in government to address [the homelessness situation at Mass & Cass], as well as other pressing issues in our city, such as transportation, public education and services for seniors and persons with disabilities.

[46][47] Flynn took particular issue with the fact that the map placed two large South Boston public housing developments in different city council districts.

[51] The map that Flynn was against was ultimately prohibited by preliminary injunction from being used in the 2023 Boston City Council election after a ruling by Federal Judge Patti Saris.

[55] In early 2022, Flynn publicly endorsed ordinance proposed by Wu which limited the hours during which targeted protests would be permitted outside of private residences, with violations punishable by fine.

[57] Flynn authored an ordinance requiring bars, restaurants, and gyms in the city to display close captioning on their television in order to accommodate those with hearing disabilities.

[62] In late November 2023, a proposal by Flynn to establish a committee dedicated to the issue of domestic violence was rejected in a City Council.

[66] In December 2023, Flynn criticized other councilors for voting against a bill that would have allowed the city to accept a federal grant for counterterrorism measures.

[70] In January 2024, Flynn revived his proposal from the previous year of creating a dedicated "rat czar" position to lead the city's pest control.

[73] In January 2024, Flynn traveled to Tel Aviv, Israel to attend a conference on the subject of Israel-Hamas War and other middle east concerns.

[77][78] In March 2024, Flynn complained of public drunkenness, property damage, and fights by attendees of the South Boston St. Patrick's Day Parade.

He proposed as a possible crowd control solution the prospect of having Massachusetts National Guardsmen patrol MBTA stations on the day of the parade.

The day following his initial comment, Flynn asserted his belief that the city had too few police stationed in its downtown, including the Boston Common.

The day following his initial comment, Flynn asserted his belief that the city had too few police stationed in its downtown, including the Boston Common.

[83] In February 2024, Flynn and Councilor Murphy introduced a resolution urging for the city to expand eligibility for Mayor Wu's pilot program that provides free admission to museums for Boston Public Schools students and their families.

[92] In March 2022, in advance of the vote for president of the City Council, reporter Danny McDonald wrote a profile on Flynn for The Boston Globe.

McDonald noted that these were attributes that had, for a long time, been characteristics of a large share of past Boston City Council members.

[29] In 2024, Flynn endorsed his council colleague Erin Murphy's unsuccessful campaign in the Democratic primary for clerk of the Suffolk Supreme Judicial Court.