Flynn graduated from Scranton Preparatory School and Marywood University before becoming a professional boxer and mixed martial arts fighter.

Flynn worked as a prison guard before winning election to the Pennsylvania House to represent the 113th district in 2012.

[11] After a complaint was filed with the United States Office of Special Counsel alleging that Flynn's candidacy and government employment constituted a violation of the Hatch Act, an attorney from the office informed Flynn that he was in violation and needed to choose between his job and his candidacy.

Flynn resigned his position with the Lackawanna County Prison and continued his candidacy.

[16] He was assigned to the House Aging and Older Adult Services, Commerce, and State Government committees.

[17] Flynn faced a primary challenge in 2014 from Scranton truck driver Lee Morgan.

[24] Flynn served on the Regional Recovery Task Force of Lackawanna County during the COVID-19 pandemic.

On May 9, 2020, Flynn posted retort against business owners who were criticizing Pennsylvania Democrats for their handling of the pandemic on his personal Facebook page, stating "Keep talking about how bad we Democrats are and WE will STOP supporting YOUR businesses.

Flynn and Representative Kyle Mullins of the 112th district both sought the Democratic nomination in the special election to succeed Blake.

[31] Following a report that the Pennsylvania Turnpike Commission failed to collect $104 million in unpaid tolls in 2020,[32] Flynn, who serves as the ranking Democrat on the Senate Transportation Committee, filed legislation to reform their method of toll collection in January 2022.

[35] In August 2013, Flynn saw a man peeking in a window of a house in his neighborhood of West Scranton late at night.

[36] On October 15, 2014, Flynn and Representative Ryan Bizzarro were near the Pennsylvania State Capitol after having a late dinner when an assailant approached and demanded their wallets at gunpoint.

He reached for his concealed pistol, a Smith & Wesson Bodyguard 380, and a spotter warned the assailant, who Flynn said shot at Bizzarro.