[2] Zirkin says he has been involved in politics since he was in elementary school, when his parents would take him canvassing while volunteering for local campaigns, including for the Smith-Greenspring Association.

[8] He won the September 2006 Democratic primary with 71.3 percent of the vote,[9] and defeated Republican Jeffrey Yablon in the general election.

[2] Media outlets described Zirkin as a centrist and political moderate[6][11][12] who frequently clashed with progressive groups, legislators, and activists.

[33] During the 2014 legislative session, Zirkin opposed a bill to reform the state's bail-setting practices to use computers instead of District Court commissioners to determine who should go free pending trial, instead supporting a bill that would add an amendment to the Constitution of Maryland to overturn the Maryland Court of Appeals' unanimously 2017 decision that prohibits judges from setting bails that defendants are unable to pay.

[34][35] During the 2018 legislative session, Zirkin introduced an omnibus crime bill that would increase the maximum penalties for using a gun while committing a violent felony from 20 to 40 years in prison, provide $21 million to violence prevention programs over four years, and repeal a law that allows defendants charged with or serving a sentence for a violent crime to be transferred from jail for drug treatment.

[37] The bill was opposed by Progressive Maryland, who called it "racially bigoted injustice" written by white supremacists that is designed for mass incarceration of Black people and "genocide".

[41] Zirkin repeatedly introduced bills to ban fracking in Maryland,[42] including in 2017,[43] which passed and was signed into law by Governor Larry Hogan.

[44] During the 2015 legislative session, he introduced a bill to hold energy companies financially liable for injury, death, or loss of property caused by fracking.

[48] During the 2017 legislative session, Zirkin opposed the Trust Act, which would prohibit local authorities from cooperating with U.S. Immigration and Customs Enforcement (ICE).

[50] During the 2017 legislative session, Zirkin introduced a bill that would prohibit the state from contracting with companies that support the Boycott, Divestment and Sanctions movement.

[61] During the 2016 legislative session, Zirkin pushed for an amendment to weaken Alex and Calvin's Law—a bill to increase penalties for people who provide alcohol to someone younger than 21 years old—by only allowing jail time and higher fines only if the adult in question "knew or should have known" that an underage drinker would drive, and if the driver caused "serious injury or death to the individual or another.

[63] In March 2016, Zirkin supported a bill to limit when the Maryland Transit Administration could use devices to record the conversations of passengers, calling it "indiscriminate mass surveillance" and an encroachment of people's privacy rights.

[66] The committee appeared to reach an agreement, but could not get the bill's new text printed before the legislature adjourned sine die at midnight.

[67] During the 2019 legislative session, Zirkin voted for the End-of-Life Option Act, which would provide terminally ill patients with medical aid in dying, after adding amendments to the bill to raise the age limit, require mental health assessments, and remove immunity clauses for doctors who offer the prescriptions.