[17] This is contrary to the argument by Morrisey's amicus brief, which said that the "EPA's overreach in the Chesapeake Bay Total Maximum Daily Load (TDML) infringes states' traditional rights the Clean Water Act intended to protect.

On March 24, 2014, in Mingo Logan Coal Company v. EPA, the Supreme Court of the United States denied the petition for writ of certiorari.

[19] The Court rejected the argument in Morrisey's brief that the "EPA unlawfully vetoed permits issued by the United States Army Corps of Engineers.

The court dismissed the case with a single short sentence: "The challenged proposed rule is not final agency action subject to judicial review.

Corps of Engineers had the statutory authority under the Clean Water Act to enact a procedure rule (Enhanced Coordination Process memorandum) to review mountaintop mining permits.

On July 31, 2014, Morrisey and attorneys general from other states filed a lawsuit, West Virginia et al. v. EPA,[36][37] in the United States Court of Appeals for the District of Columbia Circuit challenging a court-ordered[38] settlement on March 2, 2011, between the EPA and 11 states—New York, California, Connecticut, Delaware, Maine, New Mexico, Oregon, Rhode Island, Vermont, Washington, Massachusetts—and the District of Columbia.

[39] In the settlement, EPA promised to issue its now-pending rule establishing standards of performance for greenhouse gas (GHG) emissions from Electric Utility Steam Generating Units (EGUs).

In August 2014, Morrisey filed a lawsuit, along with 11 other states, challenging the EPA's proposal to regulate coal-fired power plants as part of then President Barack Obama's plan to mitigate climate change.

On October 21, 2014, the U.S. Court of Appeals for the District of Columbia Circuit denied Morrisey's Motion for Expedition of hearing on challenge to Clean Power Plan,[49] which he filed on September 3, 2014.

On September 9, 2015, the U.S. Court of Appeals for the District of Columbia Circuit refused to grant Morrisey's request for an emergency stay in the Clean Power Plan.

On January 21, 2016, the U.S. Court of Appeals for the District of Columbia Circuit denied Morrisey's request to halt implementation of the Clean Power Plan until litigation concluded.

On April 15, 2013, the U.S. Supreme Court refused to hear an appeal in Kachalsky v. Cacace, which challenged a New York law that requires a person to show a particular need to obtain a permit to carry a firearm outside the home.

[69] Morrisey and other state attorneys general had submitted a brief challenging the lower court decision, saying that the law "does not survive any level of scrutiny".

[80] Morrisey and other attorneys general had filed an amicus brief saying that the ruling by the U.S. Court of Appeals for the Seventh Circuit was a "threat posed by narrow judicial construction of the Second Amendment to their citizens and policies.

"[81] On April 7, 2015, the U.S. Court of Appeals for the Seventh Circuit had dismissed Morrisey's arguments, saying: "Assault weapons with large-capacity magazines can fire more shots, faster, and thus can be more dangerous in aggregate.

[86] On December 8, 2020, Texas Attorney General Ken Paxton sued the states of Georgia, Michigan, Wisconsin, and Pennsylvania, where certified results showed Joe Biden had defeated Trump in the 2020 presidential election.

The news came after West Virginia Governor Jim Justice, who had yet to congratulate Biden for winning the presidency, said Trump called him to discuss the lawsuit.

[100][101] Election law expert Rick Hasen called the suit "the dumbest case I've ever seen filed on an emergency basis at the Supreme Court.

Senator Ben Sasse said it "looks like a fella begging for a pardon filed a PR stunt", in reference to Paxton's securities fraud charges and abuse of office allegations.

[105] West Virginia Democratic Party Chair Mike Pushkin has called Morissey an "ideologue" and "true believer" who is likely to push "a very aggressive conservative agenda".

[116] Morrisey asked West Virginia lawmakers to consider an "anti-retaliation" program to eliminate negative consequences inflicted on prescribers who refuse to issue opioid medications, which passed in 2018.

[121] LGBTQ issues Morrisey advocated a 2021 law prohibiting transgender athletes from competing in West Virginia and repeatedly defended it in court as attorney general.

[106] He has said he will ask the U.S. Supreme Court to review rulings that found the state's refusal to cover certain health care for transgender people discriminatory.

[106] In July 2017, Texas Attorney General Ken Paxton led a group of Republican attorneys general from nine other states, including Morrisey, plus Idaho Governor Butch Otter, in threatening the Donald Trump administration to litigate if Trump did not terminate the Deferred Action for Childhood Arrivals (DACA) policy that President Barack Obama had put in place.

"[124] In June 2018, Morrisey was among Republican candidates for the U.S. Senate seeking blame the Trump administration family separation policy on their Democratic opponents.

[126] Eventually, Cardinal Health settled a lawsuit brought by the state attorney general's office by paying a $20,000,000 fine for violating consumer protection laws.

[128] According to The Charleston Gazette, "Morrisey, a former lobbyist for a trade group that represents Miami-Luken and other drug distributors, inherited the lawsuit in 2013 after ousting longtime Attorney General Darrell McGraw.

[106][130] In 2017, Morrisey joined a coalition of 50 state and territorial attorneys general in pushing Congress to pass legislation that would affirm that all law enforcement agencies retain their traditional authority to fight sex trafficking.

In a letter to Congress, the group asked to amend the Communications Decency Act to legally confirm that states, localities, and territories retain authority to investigate and prosecute child sex trafficking criminals wherever they operate, including online.

[137] He defeated State Delegate Moore Capito in the Republican primary[138] and Democratic nominee Stephen T. Williams, the mayor of Huntington, West Virginia, in the general election.