[3] In his first term, Frosh joined Karl Racine, attorney general of the District of Columbia, in filing a lawsuit against Donald Trump, alleging he had violated the foreign and domestic emoluments clauses of the U.S.

[6] As both a delegate and senator, Brian Frosh has represented Maryland's District 16,[7] which includes parts of Chevy Chase, Bethesda, and Potomac.

[17] As senator, Frosh worked to draft the law that provides a waiver of tuition and fees to state universities for children in foster care.

He sponsored bills protecting the privacy of citizens' personal information in Motor Vehicle Administration files and authorizing Maryland's Attorney General to prosecute violators of Federal anti-telemarketing regulations.

[25] Former Senator Frosh has also sponsored bills banning minimum price fixing and creating new tools to crack down on people who defraud the State's Medicaid program.

[40] Frosh is leading a coalition of 12 state attorneys general opposing the federal government's plans to expand the scope of offshore drilling for oil and gas, including in waters off the coast of Maryland.

[41] Frosh joined other state attorneys general in an effort to block the Trump administration from suspending higher penalties on automobile manufacturers that fail to comply with federal fuel efficiency standards.

[42] He also is part of a multistate coalition challenging EPA's decision to roll back greenhouse gas emission standards for cars and light trucks.

The agreement settles an enforcement action for the auto manufacturers' use of "defeat devices" in certain models of their vehicles in violation of Maryland's air quality control laws.

[48] He has also joined lawsuits against Trump over a citizenship question on the 2020 Census, the Emoluments Clause, greenhouse gasses, regulatory rollbacks, vehicle emissions standards, airplane noise, contraception coverage in health insurance, regulation of for-profit colleges, offshore drilling, Obamacare subsidies, what he described as Trump's "attempts to sabotage" Obamacare, air pollution, his declaration of a national emergency at the Mexican border, and pesticide labelling.

[59][60] In January 2019, a former Maryland Delegate filed a lawsuit against Governor Hogan and Frosh relating to a violation of First Amendment rights.

Specifically, through an executive order, Maryland has banned citizens who support the Boycott, Divestment and Sanctions (BDS) campaign from bidding on state contracts.

[62] In October 2019, Frosh authored a legal brief[63] in opposition to Adnan Syed's petition for writ of certiorari to the United States Supreme Court.

[64] In late 2018, according to HBO, Frosh offered Syed a plea deal for his conviction that would have required him to admit guilt and serve an additional four years in prison.